How can I prepare for the grade 12 English diploma exam (details inside)?

I usually get dizzy and anxious and I run out of the exam room and run away into the school hallway, leaving the exam unfinished, and questions skipped. I have an opportunity to write the English 30 (grade 12 ) exam once every four months, for $26.75 . How do I learn to calm down and at least stay in the whole time period and not run out and go home?
I am in Alberta, and I have a 65% in English 30 and I was told that if I can get 5% more (70%) I will get a second chance to go to university. If I can’t get the grades then I can just take educational psychology classes online at Athabasca university.

Edit… I do well in class so It might be in my best interest to retake the whole grade 12 English class in summer school