As per new  eligibility criteria  from this session, Candidate should have secured at least 75% marks in the 12th class examination, or be in the top 20 percentile in the 12th  class examination conducted by the respective Boards. For SC/ST candidates the qualifying marks would be 65% in the  12th class examination for NIT/IIIT/GFTI admission.

So if don't come in top 20 percentile of your 12th board then you won't be eligible for NIT/IIIT/GFTI admission.

Apart from above institutions, you can apply for other institutes as per their eligibility criteria.