Engineering Entrance Exam

If you have scored more than 75% in your 12th then only you are eligible to get admission there.
Your JEE score is good, you should try for highly preferred branches.
For your convenience, I am attaching a link here which will give you more information regarding VNIT:
https://www.shiksha.com/college/vnit-nagpur-visvesvaraya-national-institute-of-technology-24399/admission

You can get admission there through JEE Mains or MHCET.
You have to score minimum 50% marks in your 12th to be eligible.
I am attaching a link which have all the information in detail.

The best books to prepare for IIT-JEE exam are-
Maths- RD Sharma and RS Aggarwal
Physics- SL Arora
Chemistry-NCERT and OP Tandon.

The best books to prepare for IIT-JEE exam are-
Maths- RD Sharma and RS Aggarwal
Physics- SL Arora and NCERT
Chemistry-NCERT and OP Tandon.

Do smart work along with hard work. And, try to revise the topic which you have been taught on the same days. Study for at least 3-4 hours daily. Clear your doubts as soon as possible, and focus on concepts. Try to solve the questions as much as possible. Trust me, You will definitely get a very good result if you follow this.

JEE Advanced is specifically conducted by the IITs to admit students.

You can get MNIT-Allahabad very easily.

Sorry to say but its a no as IIT strictly says at least 75% in all subject mean above 75% or 75% not less than it and as you said you are from CBSE, then you won't came in top 20 percentile because top 20 percentile of CBSE is above 85%. So, you try in any other college.
All the best.

If fee is a constraint for you, then opt for UIT RGPV and it's a decent college too with average placements but to know the exact scenario for faculty and placements get in touch with the current students through social media or in person.

You should be in top 5 thousand rank for getting admission in dtu and nsit if you belong from outside delhi.
It means you have to score more than 240 marks.