Engineering

Yes, you surely can do that. Diploma in IT will not help you to start from 2nd year, but it will definitely help you to understand the vast syllabus of B.Tech. But, in my opinion regular courses are always better than any distance course. Good Luck.

After completing class 12th Science, you can apply for BS - MS programme of different IISER, IITs, NITs etc. They also offers Engineering Programs like BE in Mechanical, Computer Science, Chemical Engineering etc. In Science, there are various numerous career opportunities, some different courses are given below :-
1) B.Sc in Aeronautics
2) B.Sc in Aerospace Engineering
3) B.Sc in Aviation
4) BE in Medical Instrumentation
In Management, different Science related courses like MBA in Pharmaceutical Management, MBA in Pharma - Biotech, etc.

Do not worry you have got a good score
But unfortunately you do not have chance to get into good nits but mostly you have a little chance of getting into north east nits,
And even you can try for IIITS
BEST OF LUCK

To be eligible to get admission for pursuing Petroleum Engineering course, you should have passed 12th standard or an equivalent examination with PCM stream or three years Diploma in Petroleum Engineering course from a recognised board/ institution. If you have checked all the boxes written here then you can surely get admission. Wish you all the luck.

Bharati Vidyapeeth College of Engineering, Katraj main campus is better when compared to any other private college as it is a Deemed University and is accredited A+ by NAAC committee. So, if you are looking for private colleges of similar status then do consider Bharati Vidyapeeth as your option.
Thanks.

As per last year, minimum percentage cutoff was follows:
General-20%
SC/ST-10%. .

It depends on the college whether it is private, government or semi government. As we know CSE has always been the top branch in Engineering, so you should expect high fee structure. You should try for NIT, IIT colleges.

Yes, there are around 160 government colleges which take JEE Mains as entrance exam. Chitkara University Institute of Engineering and Technology, MIT World Peace University, Pune. BML Munjal University, Gurgaon. Delhi Technological University, Delhi. Motilal Nehru National Institute of Technology Allahabad. Jadavpur University, Kolkata. And similarly.

To get into IITs you should get through JEE Advanced. With your given percentile I wish you would get into any IIITs.

IITs are always very good and for CSE department IIIT-Hyderabad is definitely very good, but I'll suggest you to go for NIT-Warangal, because of the better faculty and better placements in recent time. All the best.