I replied to your post on the Anxiety forum but in my experience, when I am anxious it is usually right before an event and at the start of the event. After I 'get going" I am fine. I took the GRE and I had anxiety about it; however, it did not last the entire four hours of the exam.

Do the prep work that is necessary (study course), roll with the initial anxiety, and then move through the test at a rate of speed that allows you to put your best answer down and then move on.

By the way, if you have made it far enough in your academic life to even consider taking the exam, you ARE competent.