Hey MoonChild!
I felt the same way, particularly in yr 11 (i think this year is a good practice for yr 12).
Here are some things I did when I was nervous about the exams, I hope they can help
-bring a book and arrive early and read beforehand
-remind yourself that you've done practice exams beforehand and you know the content
-positive self talk thoughts (YOU'RE GONNA SMASH IT! )
-avoid talking to other nervous people who are trying to read through notes beforehand
-yoga (Idk about nerves, but it helps you feel more awake and energised in the morning)
yoga suggestion (I did this before my oral exam)-get a good sleep
-remember everyone else is feeling nervous too you aren't alone
-smile (I started doing involuntary crazy smiling before my first exam and I reckon it helps a bit maybe as an outlet for nervous energy and also makes you feel a little confident)
-this might be a weird thing but I tell my family not to say 'good luck' to me because I find that it triggers nerves in myself, (this might be just me though?)
YOU ARE GOING TO DO GREAT DON'T LET YOUR BRAIN TELL YOU OTHERWISE