Hello aspirant,

Admission to IIT's are done on the basis of JEE advanced marks and in NIT's are done on the basis of JEE main marks. Also admission to this colleges depends on various factors such as category, home state quota, branch, number of students applied, number of seats, etc. So with the rank of 1261 in sc category you are having some chances of getting CSE in any of the IIT . Though you get it in some lower IIT only as the cutoff for CSE branch is very high.  For a more clear understanding you can go through the previous years cutoff for IITs and NIT's.

You can also use the college predictor

Link- https://www.careers360.com/college predictor

Hope this helps.

If any queries feel free to ask.

All the best!!

Regards.