Dear aspirant;

Generally, for a student of any category, the marks greater than or equal to double the cutoffs of his/her particular category are enough to get them into an NIT.

Mind you, I’m talking about any branch in any NIT, not a top NIT or a good branch. For that, you’ll have to work a bit harder than that.

Simplifying the answer:

GEN ~ 200

OBC ~ 160

SC ~ 120

ST ~ 100

If you get greater than these marks, then you are likely to get an NIT.

all the best for your future.

Well sorry to say but 50 marks aren't enough to get nit through jee mains but as you're from SC category it may proved to be a rank booster but still we aren't certain about your rank as it depends upon various factors like number of applicants fill the form, number of applicants finally appeared in the exam, number of questions asked in the exam, difficulty level of the exam, performance of the candidate, previous year's cut offs trends though you may clear the cut off for your category and become eligibile to give jee advance so there are two options you have right now, 

Either to go for admissions in private colleges like SRM, VIT, GU, MU BITs etc or if you have filled to forms of other enterence exams you can go for that too

Or you should focus on your jee advance paper or try to score as much as possible in that.

So all the best!!