Very few people look exactly symmetrical on both sides. I don't even think people would notice a visible difference, but I think we are so hard on ourselves and how we look that we see even the tiniest discrepencies... :-/
To correct it, you'd have to do a lot more abwork. Or you could just accept that you're like most folks in the world and live with it. Be glad you can see your abs!
lots of people have asymmetrical abs, and in most cases, this can't be fixed by different training. It is normally due to genetics deciding how your abs will be 'shaped'. It's nothing to worry about. If you can see your abs, your fine.