Dear Chris,
How's it going?I have recieved your email.Now I am writing to tell you my thoughts.
Since I am going to graduate from senior high school,I can understand what you feel.But don not be so stressed.our teacher said to us that being nervous would lead you to the wrong direction.If you have a good emotion during the exam,you would always get good grades.
Here are my suggestions when you get stressed.Taking a deep breath is a good way to release yourself,also is the most effective.In your spare time,you can have a long walk to get close to nature.
Only in this way,can you get yor ideal grades.