Hi there. 

There are many institutions that provide admission on the basis of your JEE mains score. Of those, NITs are most reputed and honorable.

They are many private institutions that provide admission based on the score of mains. Different states and different universities have different cut offs depending on many factors but yes surely you will be getting admission in some college or other based on JEE mains score.

But try to score as much as possible in Mains to get into NITs. 

Hope this helps.

If you did not score well in JEE advanced then most probably you won't get any rank in JEE advanced so the rest of opportunities left with you is NIT IIITS GFTI on the basis of  of JEE main rank depending upon the ring which you got 100 marks you will be offered a seat so based on various quota such as category category state and course of your interest and weyou will be offered a seat