I think you are putting too much pressure on yourself due to other people's comments about your abilities. Which isn't always a bad thing as it can be a superb motivator. What you must keep at the forefront of your thoughts is that everyone makes mistakes. Everyone. Even the people scoring you. School is a place to make mistakes and learn from them. When you make mistakes, you get valuable feedback that you can apply when it really counts! I know it is easy to get caught up with the grade, but in the long run, they really don't matter. What matters is that you learn the correct way and can apply those skills after the test!