I had a one backlog in graduation (cleared); will I get rejected in the IIM Calcutta interview?

No, IIM Calcutta does not usually reject you just because of a backlog in graduation provided that you have cleared it.

Majority of the batch consists of students from top colleges like IIT,NIT,BIT, DTU, etc. It's very common for a large number of students if these colleges have at least one backlog.

I have seen many cases where people receive calls from IIM Calcutta despite having repeated most of their courses. 

So no, a single backlog will not be a hindrance for your call from IIM Calcutta.