I don't know if you know this, but it is not a good idea to re-shoot if you do a fur shot, because you really don't know how much insulin got into the cat and you just don't know if you will send the cat too low.
I have heard that green beans will bring BG down in humans, I don't know if it is the same for cats, but if so give him green beans if he will eat them. LOL! When my husband told me about the green beans, which he learned from a friend who is diabetic, I tried to get Sammy to eat them, but he just wasn't haven it. LOL!
Definitely learn how to do the fluids at home. Fluids can really help to bring down those high numbers. Check out Sammy's spreadsheet to see how his numbers came down on fluid nights. we did find that we had to give the shot on the side of the belly and the fluids in the scruff. When we gave the fluids and the shot in the scruff, even if they were on opposite sides, he dropped really fast. Also, even though Fluids can help bring the BG down it won't keep it down so insulin is still needed to help regulate the BG.
Hopefully you can get Otto to eat, I know how stressful that can be.