Hi @HayB1982 ! Welcome to THS and the forum!
There are many sitters experienced administering injections. I am one.
As @Lassie suggests, if you add your profile to your forum profile, forum members will give you feedback that will help you connect with the right sitter. Here are the instructions for doing that: How to add your listing or profile to your forum profile
Here is another topic where insulin injections are discussed.
https://forum.trustedhousesitters.com/t/cat-with-diabetes
With a good listing, I don’t think you’ll have a problem finding a good sitter.