Once you have completed BCA, then you have nothing to worry about your 12 level subject combination. Any BCA degree student with score above 50% in graduation is eligible for the course of MCA. So you are eligible for the MCA if you complete your BCA with greater than 50% marks.

In some institutes, the Mathematics in 10+2 is required for those student who have done any other degrees in sciences and wants to take admission in the MCA course. Don't confuse yourself with that.

BCA graduates are eligible for the MCA only if they have the percentage marks as specified by the MCA offering institute (in general, the minimum marks of eligibility is around 50%)

For more information regarding MCA consider the link below:

https://www.careers360.com/courses/mca-master-of-computer-applications

I hope this helps. Wish you a great eve!