Hello aspirant a rank 20k in general category is not that a big deal. You cannot get branches like cs or ece in big NITS using this rank. However you can get these branches in the new nits and a good nit if it is in your home state. 

I hope this helps you.

This link will give some idea

https://www.google.com/amp/s/engineering.careers360.com/articles/jee-main-cutoff-for-nit-trichy/amp

Hello.

You could use the college predictor to know your chances of getting into various colleges:

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

This rank may vary as only the best of the scores of the two exams will be considered for the final rank list.

Good luck!