Hi Dhruv,

At 247 marks in JEE Main examination held on 18 March 1st shift, your percentile would be around  99.84 - 99.92 percentile and your rank would be, considering 99.92 percentile - it would be AIR 818 - 920. And considering 99.84 percentile your rank would be AIR 1637 - 1840. Now, as per the previous year cutoffs you will easily get CSE branch in any of the top 5 NITS.

Refer here for more info - NITs JEE Main Cutoff 2021, 2020, 2019, 2018, 2017 - Check NIT B.Tech Admission Process, Opening and Closing Ranks (careers360.com)

To check your accurate chances in NIT, you are required to use JEE Main College Predictor Tool:- https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer

Feel free to ask doubts in the Comment Section.

I hope this information helps you.

Good Luck!