It's very common to favor the dominate side of your body... that's why you have some "asymmetry" going (think that's the right word...lol.. brain is fried).... When you box, do you use your right arm a lot? if so, you need to work on the left side the same amount as you do your right... You can get muscle imbalances everywhere in your body... You just need to make sure if you work one side or muscle, you have to work the other side....
But as far as getting your abs "symmetrical", just work both sides at the same time...(aka crunches and other exercises that target the rectus abdominis)...