Well, if one side of your abdominal wall is more developed than the other than either you have poor nerve innervation to one side of your abs or, you are somehow favoring one side during ab exercises.
You can try using more concentrated focus on the weak side during any and all ab work and also can try some twisting crunches, twisting rope crunches, and twisting leg raises to the weaker side to see if you can equal up the development.
Add 3-4 sets of twisting work for the weaker side after each normal ab workout.