Don't be nervous, be calm. Math exam is not equal to homework. It has an environment. If you can solve some problems for your classmates in class or give lectures on the stage, you can restore your confidence and make your exam more energetic. Secondly, find an opponent as powerful as you and play a game with him, which will make math as exciting as playing computer games. Finally, like you, I didn't listen to the class carefully from primary school to high school, but I would copy down the teacher's questions in class, skip what I could do, drill if I couldn't, and even ask your competitors. It's important to do more and learn more at ordinary times. I hope it helps you!