First of all in college don't mess up with your studies. Try to score above 80% in graduation college because 10th 12th and graduation percentage is one of the important parameter used for forming your aggregate score which is used to make up a merit list and call students for next round of interview and WSAT. Among which academic records has a weightage of 10-25% and in this also graduation percentage has highest weightage. So if you could score good percentage in graduation then you can cover up the loss of marks due to 12th percentage.

Also if you are interested in MBA so much then start preparing for it slowly along with ur graduation studies.

You have lots and lots of time more than enough for preparations. Give more than enough time to master your basics in all the 3 sections. Don't worry about the result right now.

Enjoy practice and learn. You have 3-4 years before you give CAT exam so enjoy and  study consistently.

All the best!!