It can take time. So do be patient with yourself. (((Hugs)))
With both of my diabetics the key to success with testing has been 'desensitization' and 'counter conditioning'.
My first diabetic was a large and strong willed cat, and there was no way I'd be able to test unless he was OK with that... My current diabetic girl absolutely hates having her ears touched, so she presented a particularly difficult challenge at first (Note: some cats are fine with paw testing, but my girl hates her feet being touched too...)
Neither of my cats has tolerated being held or restrained in any way at all. So, I've had to use 'distraction' to keep them relatively still while I quickly test.
I could distract my first diabetic with some crushed cat treats and test him while he was hoovering up the treat crumbs. My diabetic girl likes to be brushed. So, I just sneak a test into the middle of a little brushing/grooming session and she barely notices. Singing to her while I brush her seems to help too...

....This did take a bit of time, but with patience and persistence all kinds of things are possible...
With both my cats I've had to go slowly, introducing just a very low level aspect of testing at first, but not enough to spook or upset them.
....This is something that I wrote for another group, just copying it here in case it's helpful...
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GETTING KITTY USED TO BEING TESTED - ‘DESENSITISATION’
Some kitties take to being tested like proverbial ‘ducks to water’, they are just not bothered by it at all. Other kitties take a bit more work, and with a minority of kitties it can take a quite a bit of dedicated effort to get them used to the process.
Please be reassured that ‘most’ kitties can be tested, and ‘most’ people can learn to do it. Honestly!
One really useful way to get kitties used to testing is to ‘desensitise’ them to the sensations and sounds involved in the test process. And a really good thing to do at first is just to get them more used to having their ears touched.
So, whenever you are stroking or cuddling the kitty use that opportunity to include very gentle ‘ear touching’ when you stroke them,
just for a second at first. Make ear touching ‘ordinary’ and nothing to fear...
You can also go to wherever the cat is chilling out, then stroke them, hold or massage an ear for a
second or two, and then
immediately reward with a yummy treat and some praise. This starts to condition them to associate ear touching with rewards. And this is what you want to happen.
You can also get them used to the test kit itself. For example, you can rattle the test strip container, or click the lancing device a few times (it can be used a bit like a training clicker), and immediately give the kitty a treat. Then just walk away, leaving them with their reward. They can soon come to associate those sounds with rewards just like when they hear the sound of the can opener...
I did these kinds of desensitisation techniques with my kitties about 6 or 7 times a day at first during the first couple of weeks. It only takes a minute or two each time, maybe only seconds. But that repetition is key to success. Repetition, repetition, repetition...
It can be often be helpful at first to test in the same location so as to establish a routine. I tested my first diabetic on a table top. I test my current girl in her favourite armchair. You can get the kitty used to the test spot by taking or calling them there and just rewarding them with strokes or brushing, or treats.
Make the test spot a place where nice things happen.
If you can get the kitty to the test spot and hold or massage an ear for a second or two and then reward with a treat and praise, you really are most of the way to being able to test on a regular basis.
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HOMETESTING TIPS & TRICKS
1. WARM EARS. Probably THE most important thing. Warm ears bleed very much more easily than cold ones. You can warm an ear by massaging it, or by holding something warm against it; ie a pill bottle filled with warm water, or a ‘rice sock’ briefly warmed in the microwave.
2. MASSAGING immediately below the ear prick, with finger and thumb, can ‘milk’ more blood out. I almost always do this, if only for a second or two.
3. VASELINE. A teensy weensy smear of Vaseline on the outer edge of the ear will enable the blood to ‘bead up’ and stops it disappearing into the fur. This also makes it easier to see the blood droplet if the kitty has dark ears.
4. RESISTANCE. The lancet needs something to ‘resist’ otherwise it can push the ear away rather than pricking it effectively. Some folks use a piece of cotton wool or folded tissue. I use one of my fingers, but sometimes do accidentally take a blood sample from myself that way.
5. TWO EAR PRICKS close together can often produce enough blood for a test when one ear prick might not.
6. SCOOPING THE BLOOD DROP ONTO YOUR FINGERNAIL. Doing this is a game-changer for some people. If you can get that drop of blood on your finger or thumb nail you can then let the kitty go and finish the test without her/him.
7. TREATS. It is important to reward the kitty for each attempted test, whether the test was ‘successful’ or not. Cats very soon learn to associate tests with treats. And some will soon come running for their tests. A ‘treat’ is usually a food reward of some kind, but some folks reward their kitties with a cuddle or a grooming session. I actually crumble a few treats for my cat and test him while he’s hoovering up the crumbs.
Remember to reward yourself too. Chocolate is good…
8. GET COMFORTABLE. If you are physically comfortable you’ll be more relaxed, and also less likely to try to rush the process. Some people like to test their cats on a counter top or a desk, maybe next to a desk lamp. Some people prefer to hold their cats on their laps when they test. Some folks incorporate testing into a grooming session. You’ll find what works best for you. And once you get used to home testing you’ll quite possibly be able to do it anywhere, and maybe even while the kitty is asleep.
9. RELAX. Cats pick up on our moods. The more relaxed and ‘matter of fact’ we are, the more relaxed and confident the kitty is likely to be. Some people chat or sing to their cats while they test him. Try it. It might help you too.
10. PATIENCE. Be kind to yourself. You’re learning something new. (And you’re learning something wonderful!)