There are many students across India, who have Physics, Chemistry, Mathematics and Biology subjects in there 10+2 or Physics Chemistry, some other combination and Biology as an additional subject and still they ,managed to get a seat in Government Medical colleges. So its nothing like that, the syllabi is the same for the additional subject and the compulsory. You don't loose something out of it. So if you prepare well for the NEET and manage to score in NEET, then you will definitely be able to get seat in Government medical college  for MBBS.,

For NEET preparation tips consider the link below:

https://medicine.careers360.com/articles/neet-preparation-tips

I hope this helps. Wish you a great day!