Hello Midasala, Greetings!

Let me help you.

If you have backlogs, then also you can write GATE exam, but before admitting to M.Tech or PSUs, you need to clear all of them.

If it is year lag, then also you can write but you cant get benefits of GATE exam. For this you need to be graduated.

You can refer to official broucher for more information:

http://gate.iitd.ac.in/PDFs/GATE_2020_IB.pdf

Thank you, best of luck.