Hi. Your combined merit rank indirectly also determines your category rank, and both are of utmost importance. Lets take two examples:

1. There are 100 seats in your college of choice. There are 10 seats reserved for your category (SC in your case). Lets say your general combined rank is 110, and considering the total seats in your college, it is difficult for you to get a seat. But say your category rank is 9, you will easily get a reserved seat.

2. If your category rank was to be 11 but lets assume your general rank to be 90, you can secure a seat in the unreserved category too.