Hello Akhilan

First of all congratulations for your result. 

According to last year's NIT's cut off at 21767 SC category rank you wouldn't be eligible to get admission in any of the NIT's.The maximum rank goes upto around 9000.

You can check last year's NIT's cut off and closing rank using this link:

https://engineering.careers360.com/articles/nits-cutoff-for-btech-civil-engineering

Also you can predict your Jee Mains college using this link:

https://engineering.careers360.com/jee-main-college-predictor

So I hope you find this helpful 

Thank you 

Good luck.