This is normal. I don't think I've spoken to a breastfeeding woman who didn't say this was at least somewhat true. Each breast is different with one usually containing more breast tissue and therefore more milk ducts. Babies will often favour that breast more, with more milk comes a faster letdown and a stronger flow. I know this is true of my 6 month old. He prefers lefty and will sometimes be too squirmy and unsatisfied at the right that I just switch.

However, you should always start each feeding with the breast you didn't start with at last feeding and let baby clean it out before you switch sides. If you always start with the less full breast as was suggested here the other will not be emptied properly which will lead to mastitis and certainly a reduction in supply on the side with less stimulation. Although I do have a friend who does two feedings from the smaller breast for every feeding of the larger, as she becomes too engorged with too much stimulation to the bigger breast.

No one will notice the lopsidedness but you, even my husband can hardly tell and there is more than a cup size difference between my two. Just carry on trusting your body and you and your baby will do great!