Dreading a program I signed up for to the point its ruining ever day of my summer break.

Hello everybody, I hope you're all doing well!

I recently signed up for the national lifeguard course to become an actual lifeguard and its a 5 day course that goes from 9 am to 5:30 pm for each day Monday to Friday. Its literally only 5 days but i have been dreading it so much. I also really really don't want to do this course but i've been doing these lifeguarding courses for a while and if theres only one course left I can't stop now. Im currently in my summer break and I want to enjoy it as much as I possibly can as I worked really hard this school year and studied a lot and now finally have a break, but I just cant stop thinking about this course. Im afraid I might not pass the course because of one of the difficult parts that I have to do but that I have been practicing, I also feel that ill be embarassed because im not the fastest swimmer and the others would probably be much quicker than me, and theres also a thing that I dont really wanna say that if it comes on time (which is a day after the course ends) i'll be fine but if it comes early (which it does a lot of the time) everything will be messed up for me, not to the point that I cant even go to the classes anymore but it'll just stress me out even more. Is there any tips from anybody on how I can stop worrying and fix my habits to be more stress-free because I know this may seem super silly to some people but I literally can't stop thinking and worrying about it to the point I think about it more than 30 times per day and its been ruining my summer break so far. If it matters the course starts this coming Monday and ends on Friday.

Thank you!