Finding TDC

So I'm trying to find tdc with a piston stop so I can put new timing tape on my balancer. I've gone through the hole process, stopped the piston, marked it, turned it the other way and marked it where it stopped. measured to the middle of the two marks. But the mark in the middle points to 10* ATDC on the marker which is on the timing cover. Did I do something wrong or am I just confused here?