I've been training with retired IFBB pro Mike Francois, he told me that I should be doing 9 sets for chest, and chest is my weakest body part.
I have the same problem with my chest, one pec is bigger than the other. It's only because one side of my torso is wider than the other, i.e., the distance from my neck to my shoulders is not the same, one side is longer than the other. It sucks!!!. I see it in the mirror every day. It will probably hurt me in competition, but I'm getting bigger, so I don't really care!