The key to dealing with any test is to prepare and relax. It is not unlike training for a sport. A hockey player doesn't wait until the night before a game to start skating. Baseball and football players practice a lot before their games. Swimmers, dancers and all other athletes train for their sports. Yet, some students expect to study just before an exam and do well.
Standardized tests and other exams have some clues to what will be on them. You can find these in your state's learning standards or on a course syllabus or school curriculum. These items can be used to prepare your study plan. Even if a teacher isn't covering everything, exams, like the regents, will cover all or nearly all the material the standards say they will. The good news about that is, you know the rules of the game. There are only so many questions they can ask on those standards or syllabus or curriculum points. You can divide the amount of time you have, minus two weeks for review, by the number of topics you have to cover. For example:
Say there are 6 weeks till the exam and 50 topics. Take 4 weeks times 5 days a week (because you need some time to relax, and meet your other obligations), that gives you twenty days. Divide 50 by 20. You get 2.5. This means you need to cover 2.5 topics a day and be sure you know them. Then you will be prepared and still have two weeks to review. That usually takes care of any nervousness.