Hey,

First of all not all IIMs give weightage to your graduation marks. Secondly, even if they consider they consider the average of the whole semester that you have studied.

If your college gives average grades of your all semester that's how will the IIMs will also consider.

You need to fill the average marks or cgpa of your all semester at the time of form filling for IIMs.

Hope that clears your doubt.

Thank you