You got 75 percentile score in JEE main then it means your rank would be around 220000 so you can think that this rank is not a good rank and the seats in NIT is limited to 30000 so it  is impossible get a seat into NIT, I would suggest you to reappear for JEE main that's jee main April and score good  percentile score to be eligible to get into NIT, to get into NIT you should score more than 97 percentile.