Can an uneven chest be corrected or less noticeable with muscle growth after a gynecomastia surgery?

The pectoral muscles are not usually involved in gynecomastia surgery.  Once your plastic surgery approves you to workout at the gym, you should be able to build those muscles with body building exercises. However, the larger/stronger pecs may not fill out the "empty spaces".Kenneth Hughes, MD, Board Certified Plastic SurgeonLos Angeles, CA

When the surgical procedure results  in uneven  breast,you should wait for 6-12 months to see the final outcome.Sometime there is a need for additional surgery. 

Sorry to hear that you have concerns after your surgery.  Unfortunately, I think it is very unlikely that building muscle will correct contour irregularities or asymmetries after surgery.  Think of the pec muscle as the mattress and the skin, soft tissue, and gland as the blanket and sheets.  Filling the mattress isn't going to make the blanket and sheets rest smoother.  Know that at 3 months, especially with secondary surgery, you are probably not looking at your final result.  Make certain to follow up regularly with your plastic surgeon and be compliant will all their recommendations to optimize your surgical results.  Best of luck!