Originally Posted by Cogito Ergo Sum

If your marks in FSc are above 80% and you want to repeat to make it between 85-90%, and you think you are capable of doing that, then repeat FSc and go for MBBS. But, if that is not the case, do BSc.

Zoology, Botany, Psychology, and Chemistry are the only optional subjects offered in CSS that are somehow related to pre-medical FSc subjects. You can opt them or you can choose any other of your own liking. While you pursue graduation, keep improving your English skills and you will be ready for CSS prep by the time you graduate.