Never been a server / waiter but I can provide some advice...
You will mess up, it's a given. It's a new job, something you've, I assume, never done before. It should be expected that you will mess up at some point.
Being afraid to mess up is just going to make you freak out when you finally do. Expect it and realize This is something new, I can't be expected to be perfect. I just have to learn from my mess up and keep going.
Good luck though with the new job! I always like to remind myself because I am a bit of a perfectionist, as long as you're moving forward after a set back, you're doing what you should be!