Hello..primarily dont get panic by the line in mouth.It is normal finding which is called linea alba occuring at plane of occlusion.

These are very normal lines which appears with fast eating habits and cheek biting intermittently . I hope there is no intake of tobacco and its product in any form. Kindly consult dentist and get treatment for your sharp cusp edges. These lines will remain for longer period of time. Nothing to worry. Chew slowly, gradually and enjoy the food.

Linea alba buccalis  is a common  finding  and not worry some

It's cheek bite and nothing to worry much.close your lips and try to blow air to keep your cheeks apart from teeth.do that regularly it will help you.