• Yes you are eligible for it. But your score must be grater than 45%.
• http://www.christuniversity.in/master-of-business-administration-(mba)/management-studies/bachelor-of-business-administration-(bba)/1077

Hi

The eligibility for a BBA in Christ College is:

• Basic eligibility for the programme is a pass at the +2 level (Karnataka PUC / ISC / CBSE / NIOS / State Boards) in any stream (Humanities, Social Sciences, Commerce & Management, Sciences) from any recognised Board in India.
• Candidates writing the +2 examinations in March-May 2018 may apply with their class X and XI marks.

Since, you have passed and are voluntarily giving the supplementary exam to improve your score, in my opinion, you are eligible. However,  you need to have at least 45% in 12th.

Regards