My pop told me "You just do the best YOU can do, and that's the best you can do!"
And then I came up with my own thing, like for things I'm scared to do (Dental Appts., exams, etc.)
As long as you're studying, when you start feeling panicky, visualize the evening, or even the day AFTER the exam. (For Dental Appts., like a root canal, I just imagine 3 hours after the apointment. It really works every time for me! I hope it does for you!