I have 15 to 20 percent preparation of jee mains till now

Hey..first of all have positive attitude in yourself. Give your best in preparation. Do hard work.Since you have coverd only about 20%, you need to work very hard. Don't think about the marks you will get, but prepare.

Now, you are left with two months. Give  your full time to jee preparation. Remember one thing that quality matters more than quantity so do smart study. Don't try to cover whole sllybus . But do good in what you cover in sllybus. Work on your weaker subject and give about 10 days for revision in last. Study more than 12 hours a day.

All the best