It is very good thing that you are great at Mathematics. Maybe the reasons for you failed in exam is because the maybe any mistakes in correcting paper or you wrote the question numbers incorrect or maybe the answers you thought right is wrong etc. There are many possibilities for that. Please don't be disappointed. If you are so sure about your performance in exams you can apply for revaluation. If there is any mistake in correction by the teachers, your mark will definitely increase.

Thank you