Try and relax, everyone has some feeling of apprehension, particularly when its something that you desperately want to achieve. I know this is easier said than done, but, try to find out what the tests are about and try some practise exercises. They wont give you the answers, but it just gets you into the idea of doing it. When you do any test or exam, just focus on doing your best, rather than worrying about how your doing, if that makes sense. Never allow thoughts of doing poorly enter your head, just go for it.
Hopefully someone will come along with more specific detail about BA.