Asymmetry is not unusual and very hard to correct. Look at Dorian Yates although one huge MF'er what made his so great was is was very symmetrical or balanced. Muscle Belly imbalance change the size and shape so you will always have one side looking slightly different. Not a whole lot you can do unless the imbalance came from non-use from something such as an accident. Working one side more has not been proven to make that side grow more and in fact could cause over training and muscle loss (making this statement based on the person already giving 100%, adding more work is not going to make it grow more.