Im guessing you meant post op too :p
My pecs are odd. My left side is more concave, like you describe. The fact that I can see a difference in the two, makes me realize even more. It does feel like he took too much muscle from that side, but what it may actually be, is the surgeon leaves a little bit of fat behind anyway, to prevent the chest from looking concaved. The surgeon explained that to me. So, he may have taken a little too much from my left side, and yours may have taken a little too much from your chest. Though, dont quote me on this, its just me guessing.
I found going to the gym helped alot to build up the pec muscle. (As, you cant really see the difference in my picture) but it is there. Even by building the pecs, the left side is still, "shorter" I dont really know how to describe it.And the left areola is concave abit, which caused it to change shape. So if I move my left arm, it stretches into an almost vertical line!
You could talk to your surgeon about it, see if he suggests anything, but I would suggest working out your chest to try to build and define your pectoral muscles.