I’m so nervous for my lifeguarding training that I can’t sleep

This is definitely important training so you have good reason to be nervous. Go through the steps in your mind until you are comfortable you know them. When it's over and you passed work on swinging your whistle.

Think of it this way: if you definitely can't sleep, accept it as fact, i.e. don't stress it (unless you can't help but stress it).

Use me for CPR training haha