Don't stress yourself out too much Michelle in worrying. Many cats tolerate higher #s fairly well even for extended periods of time, and though of course that is not ideal, if Prudence is eating well and acting ok, and you are checking her pee daily for ketones and the readings are negative, it's nothing to lose sleep over. If she is not eating, or acting like she feels rotten, that's when it gets more worrisome.
We've all been where you are - everything is new and overwhelming, and every # - high or low, is a reason to freak out! You will get a better feel for things as you continue and it will get a lot easier.
You are right not to give a second shot if you are unsure the first went in. If you don't know if it was a fur shot or not, just put that in your spreadsheet notes, but don't shoot again, it's really too risky if it did go in. Even if you felt some liquid in her fur, you wouldn't want to shoot again, as you wouldn't know if you got a partial shot in or not, or how much might have actually gone in.
You are doing great, just follow along with Terri's advice on the dose, and continue to ask questions if you aren't clear what to do. You are seeing a good response to the insulin, so it just takes some fine-tuning from here to get her in good #s more consistently. Yes, she can still go OTJ regardless of feeding patterns, and smaller meals more often is supposed to help their pancreas by not overtaxing it all at once.
You have gotten good advice about dosing and ketones from the others, so I will just address this question you had about meals. It is actually best for a diabetic kitty (and all kitties, really) to eat many smaller meals throughout the day. This keeps their pancreas from being overwhelmed by a lot of food at once. If the pancreas works at all, food will stimulate it, which will, in a perfect world, bring down BG.