I am past the age of exam taking; but, I took them very seriously. Without a good education, your prospects of a good-paying job are limited. I had confidence by preparing for several days ahead of time with extra studying. I would try to envision the types of questions that would be asked and studied accordingly.
My confidence then came from knowing that no matter how I did on the actual test, I had prepared enough that I would be giving it my best effort. As long as I did my best, I was fine with the results.