No one's body is symmetrical. If you took a picture of yourself and cut it in half and duplicated and flipped over each half, and then pieced them together... you would see you would look totally different with 2 left 1/2's being put together, and 2 right 1/2's being put together. The same goes for our arms, legs, breasts, feet.
I wouldn't worry about your skull. If your skull were exactly the same on each side you would be in the medical history books as an anomaly