You'll get admission according to your only not just marks and rank depends on many other factors like difficulty level of the paper, number of applicants appeared, last year trends,number of the seats so first you need to calculate your rank and you can do it with the help of the JEE main rank predictor of Career360.

https://engineering.careers360.com/jee-main-rank-predictor

For top NITs you need a rank below 10k but if somehow you'll manage to get a rank below 20k you still can get into some NIT else you can try for other colleges that take admissions thorugh mains you can go through the cut offs for different colleges including NITs of last years.

https://engineering.careers360.com/articles/jee-main-cutoff

ALL THE BEST!!