I don’t know how to help you stop the blocking but I strongly encourage you to email your teacher. She probably thought you were nervous more than dumb. You can explain to her in writing whats going on, if she’s good she’ll accommodate you. At the least she won’t be confused. If this was a substitute and you won’t see her again, email your regular teacher. Do it in the future with new teachers. You are definitely fit and worthy of a good education. Remember that people like Helen Keller were able to pursue higher education, so can you.