First of all congratulations!!
If you have got a call from IIM AHMEDABAD then that's a great opportunity for you to convert.
See, you need to know one thing that IIMs don't send calls randomly. They go through a standard process before sending out calls. And if you have received a call then it means they would have seen something strong in your profile. So currently do not worry about 10th marks. It's just one class that might show low scores, they might ask reason for low scores in this class, you just need to justify it honestly.
A lot would depend on your interview and WAT.
All the best

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