It’s not at all necessary to be an IITian or a topper to get admission to IIM Ahmedabad or Bangalore. Some students are neither batch toppers nor IITians. In fact, some of them do not even finish first in their class in 12th grade.
You must perform well in interviews (both IIM A and B), have a good CAT score, and demonstrate consistent academic performance. And consistent academic performance in college means a CGPA of 9.1/10.