Hi Josieee....Sitting an exam is a moment in time..during that time you need to be calm. Your mind has all the information you have learned stored and ready to be used. Allowing your mind to relax enables that stored information to be accessed easily. When you sit down in the exam room take a minute to breath slowly, pausing briefly before you exhale. Do this 6 or seven times and repeat during the exam when you are finding things difficult. This will calm and relax you and bring your thinking into the moment.
I hope this helps.