Fighting is wrong. Most parents treat their children who have done something wrong in this way. But what you did was wrong. Your mother hit you because she was angry. You shouldn't lie to your parents if you don't get good grades. No one can do well in the exam every time, but only if you work hard at ordinary times. If you work hard and don't do well in the exam, tell your parents that they won't blame you. But you cheat teachers and parents by cheating. This question of principle is definitely wrong.