Hello!

You can only get admissions into NITs on basis of your JEE Paper score, not through your board marks. Althought your board marks have to be a mimimum aggregate to get admission, it is your JEE exam marks which have the main role in getting you your admission. For NITS heres a link for closing ranks if you've appeared for JEE

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

Good luck!