If you are in top 20 percentile than you are eligible also for the jee mains.
One of the criteria either percentage criteria or percentile criteria must be fulfilled by a candidate.
So good luck.

Yes a candidate must acquire minimum 75% in 12th standard to get admission in any of the branches of engineering in any NITs across India with Physics, Mathematics and Chemistry and compulsory subjects. 

A candidate must also score high marks in JEE Mains so that he/she can get a branch of his/her choice. 

If you still have any queries feel free to ask in the comment section down below.