No caffeine. It will increase your blood pressure and make your heart beat faster.
Try to get enough sleep every day, especially a week before the exam. It will help with your mental clarity. This sounds easy but it's really hard for a lot of people.
Change your way of thinking. I know GPA has some weight in them but they don't follow you for the rest of your life. It's okay to be imperfect as long as your average result shows improvement as time goes on.
Remember, you learn for yourself, not for the GPAs. Instead of thinking "I will probably fuck up so bad / If I fuck this up my career is over", think "I have learned my materials and now I will try my best. Let's see what will come out of it."
Box breathing to regulate your breath:
https://www.healthline.com/health/box-breathing#tips-for-beginnersIt works for me. But you need to practice it everyday because the first few times you try, you will feel dizzy.
