Dear Betty,
Knowing that you care too much about the result of the coming exam, I am quite worried. Actually, the most important thing is not the result of the exam but the learning journey.
There are some effective ways to calm down. First, keeping reminding yourself to stay in peace is the most helpful. Second, it will help you to relax if you spare some time doing some after school activities like sports. Finally, talk to your parents and friends, who are always ready to comfort you. In a word, the result itself is not really important, but we should work hard while learning.
Yours,
Joe