You haven't scored good in jee main however with your category rank you'll be able to get admission into the top NITs and even get the core brances like CSE or ECE as the results are announced recently the cut off rank for different nits and colleges are still not out but they will be soon till then we can't be absolutely sure about this years cut off but a rank around 18-20k will surely be able to give you admission in some good NITs with your desired branch. You may predict the colleges you might get with this rank with the help of our jee main college predictor you just need to enter your all india rank,your category, your home state and your desired branch and you're good to go. I am providing you the link for the predictor, 

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