JoSAA

You should not be below 20-22k general rank in order to get admission in IITs in OBC-NCL.

Chances for getting in NIT or IIIT via JoSAA is too low for this rank bracket. You can try for other good colleges.

You should choose state colleges as you will be getting better specializations over there.

If your JEE Mains OBC rank is 45001 then you should apply for 2nd tier college because at this rank you are eligible for NIT college and the best colleges are BR. Ambedkar College and Kurukshetra college as this is best colleges.

With an OBC category rank of 142621 in JEE Mains you might get a seat in following colleges with CSE:
IGDTUW-Indira Gandhi Delhi Technical University for Women
K. J. Somaiya College of Engineering, Vidyavihar, Mumbai
Shri Vile Parle Kelvani Mandal's Dwarkadas J. Sanghvi College of Engineering, Vile Par

When you pay, you get the receipt, there it is mentioned if it's refundable or not. You can talk to the management for refund, you can tell them the reason for withdrawing.

JoSAA 2021 cut-off for IITs:
IIT Bombay: 4 Opening rank and 5976 Closing Rank.
IIT Guwahati: 425 Opening rank and 8994 Closing Rank.
IIT Delhi: 31 Opening rank and 6278 Closing Rank.
JoSAA 2021 cut-off for NITs:
NIT Calicut: 4 Opening rank and 47595 Closing Rank.
NIT Meghalaya: 626 Opening rank and 42

In Joint Seat Allocation Authority (JoSSA) counseling, seats are allocated on the basis of the merit of the candidates, category, availability of seats, and select preferences by students. Students who will be allotted seats have to download the provisional seat allotment letter and an e-challan to

Joint Seat Allocation Authority JoSAA counseling will be conducted online in six rounds. Qualified candidates of JEE Advanced will be eligible for admission to the Indian Institute of Technology (IITs) while students who qualify for JEE Main will be eligible for admission to the National Institute o