Hi Nitesh

You can get admission to NITs, IIITs, IITs & CFTIs by fulfilling these three conditions:

If you have valid JEE Main scores

If you have 75% scores in class XII or

If you come in top 20 percentile of your class XII board

In your case, when you are saying that you were unable to score 75% in class XII, your last escape is to be in top 20 percentile in your board.

Also, when you are talking about admission to NITs, you will get only 50% seats because of home quota.

Refer to the link given below to know about top 20 percentile across NITs.

https://engineering.careers360.com/articles/top-20-percentile-of-class-12-boards-for-nits-iiits-and-cftis

Hope this helps!

All the best !!