Hiya, Turt,
First shot jitters are a lot like dreading most other things, once it's over, you'll wonder why you got yourself all riled up.
Don't sweat it, it's just one more thing to add to your routine. Quite frankly, my dear, it's much easier than changing a poopy baby!
If you want to practice, just get out a needle and take a few pokes. Honest, you'll get used to it, trust me!