I was going over my bike and I noticed the inside of the sprocket was getting worn down badly. I thought I had the axle on crooked so I counted the marks on the blacks. They were the same number of marks from the front, but I took a closer look and noticed there were more marks on one than the other. Are these suposed to be different and is my axle crooked? I am 4.5 marks from the front on each side. The sproket wear on the inside of the sprocket tells me I have a problem.