Hello Abhinav,

It is difficult to predict your exact qualifying marks or admission possibilities to get into top NITs as the exam is being conducted twice in multiple session first time and the final NTA scores will be used to rank the candidates. 

You can use this formula to calculate your expected rank-

874469 are the number of candidates appeared for the January exam. So rank formula is (100- your total score) * 874469 / 100.

If the number of candidates for April exam increased to 1400000 then your final rank shall be (100- your total score) * 1400000/100

You can also check your admission possibility with the given below JEE Main college predictor.

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

Good Luck!