Well brother, I can understand your situation. I know you have worked hard for JEE mains but I believe with 12.8k category rank you won't be getting decent college which I can recommend you.

Though with OBC and home state quota, there might be an increased chance of your's getting a seat but with such a rank it is very hard to get.

As, opting a very a bit low mideocre NIT will bring nothing good for you.

 You can prefer state engineering colleges. Some state eng. colleges are way better than even mediocre ranked NIT.

The best possible NIT available 

1. NIT Raipur (though chances are really very poor)

Also, I would recommend you to do take part in JoSAA and go to through all the round even the spot round. May be, some good fortune can turn your destiny. 

Thank You