After 12th you need to go with your bachelor degree. If you completed your graduation and want to get admission in MBA program doesn’t matter what is your percentage in your 12th.

MBA admissions are based on entrance exam. If you successfully clear in entrance exam then you can do MBA after low marks in 12th.

For MBA admission with low marks you need to enter some extra impact for admission:
A combination of one or more of the following actions may help you offset the impact of a lower academic performance.

Get a high GMAT Score to counter low GPA

Select the right B-schools

Take extra courses

Use the Optional Essay well

Position yourself as a strong contender

Find a Study Table, Prepare for CAT, MAT, CMAT, XAT etc. and you will definitely become a good manager in near future.