BCA

Admission at 45% in Mba is possible from OBC section at MIT Pune, BIMM, Symbiosis.
check list for colleges.
https://www.shiksha.com/mba/ranking/top-mba-colleges-pune/2-0-0-174-0

both branch are totally different bca stand for computer science and bsc biotechnology is medical science .you opt any one over your interested field. both branch are interesting.

Pure IT is some what different from MCA but in context to career its good choice i e BCA+MCA.

yes it includes maths

With NIIT you will certainly stand to gain more than what you were with mere BCA Priyanka. But then learning is one thing and application of it is another thing which you need to do very skillfully to succeed in a job. I suggest that simultaneosuly you must also enhance your other abilities such as communicative ability, language etc which can help you in cracking interviews in a better manner.

After BCA you can do M.C.A from IITs or jawahar Lal Nehru University or other premium institutes. I think Gate is not required for IITs but JAM is the test but to be sure you should visit any IITs or Isc Bangalore website.

No i n the Field of computer line you must pass in Maths
so improve your result and try again.

No, it's on you how you done it
I am doing Bsc(CA&IT) i saw that both is similar but in Bsc you'll work Hard.