Hey Aspirant  ,

I want to tell you that at 20000 rank the chances of getting into nit , iiit or any other government college is quiet low . You might some lower nits or iiits with lower branches but that's also not sure. So what I would suggest that you should go for private colleges like

1 . VIT Vellore

2. SRM Chennai

3. Jaypee University Noida

4. Thapar University

5. Manipal Institute of technology

These colleges are also a good option for you and you might get CSE also.

For further reference I am providing you with a link to predict a college through JEE Mains

https://engineering.careers360.com/jee-main-college-predictor?utm_source=qna&utm_medium=jee_cp

I hope this helps!!