You haven't score a very good rank but as you told you're from SC category so it boost the chances of you getting admission through jee mains but the chances of getting cse in NITs are still very low as there cut offs are very high even for a SC student but don't you worry there are many colleges who have jee main reservations in them and some percent of seats are reserved for the students who're taking admission through mains you'll easily get cse in them you can see what colleges you might get with this rank with the help of our jee main college predictor you just need to enter your rank your category,your home state and your desired branches and you're good to go and you can even have a look on previous year cut offs of NITs and other colleges. I am providing you the link for all. 

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

https://engineering.careers360.com/articles/jee-main-cutoff-for-top-nits

https://engineering.careers360.com/articles/jee-main-cutoff

Good Luck!!