Hell dear, according to your percentile in jee mains your general rank will be in between 20000-30000.With this rank you will definitely get seat in NIT  but also you have to score 75% marks in higher secondary examination conducted by respective boards  also you be in top 20 percentile. You have to improve your marks in order to get seat in NIT. 

Hope you understands. 

Good luck 

Hello,

 Qualiffying in JEE mains is not only the requirement for getting NITs you need to clear your boards with atleast 75% marks,so on my opinion you need to improve your boards marks first.98 percentile is a good score i think you can definitely get admitted to college after improving your boards marks.

Best of luck!!