JEE Main Scores

Sorry to say dear, but these marks are not enough to fetch you a college.
I would suggest you to go for any private college having good placement records.

You can predict your rank and college with the help of the links given below:
1. Rank predictor: https://www.shiksha.com/b-tech/resources/jee-main-rank-predictor
2. College predictor: https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

Depends on your category. If you belong to SC or ST category, then you can get good college.

You have got good marks, but NIT, Surthkal, Karnataka comes under the top list of NITs.
Not only this, they both are famous for their mechanical branch after NIT, Durgapur and Surat.
So, 139 is not enough as the admission in those NITs starts from 180+ for home quota and 250+ for other state students.
But as you mentioned you are an OBC category student, you have very slim chances to get into it.
I will prefer to give them top priorities in the choice filling.
All the best.

Yes, if you have cleared the cutoff score for SC category students, which is given below your score card.

There are many good engineering colleges in Indore, Bhopal and Jabalpur. You can look for any of the engineering college in Indore, Bhopal or Jabalpur.

It will be difficult for you to get into Nirma University with this score.

Sorry dear, but 21 marks are not enough to grab you any govt. college.
You should try for any private college which offers admissions through direct means instead of JEE Mains rank and score.
All the best.
Please upvote my answer.

If you are qualified, you can apply for NIT counselling through www.josaa.nic.in.
The same counselling is valid for all NITs, IIITs and also GFTIs.
To get the colleges other than NIT, IIIT, and GFTI, select the colleges where JEE Mains scores are accepted and just fill up your JEE roll no. and marks in the application form so that you can get admission.
All the best.

Since this exam is conducted only once a year, there are no chances to write this year again, but you can appear for the JEE mains exam the next year. Maybe if you take the exam next year with full focus then you can get IIT.
All the best.