As I stitch a large quilt using a pantograph, I notice that consistently the layers, even though I know I have them squared on the rollers, shift to the right when standing at the back of the machine. I consistently am starting the right side of each pantograph row further into the right and ending on the left side before I've reached what was the original marked start. The quilt is pulling to the right each time I advance it even though I mounted it squarely. What am I doing incorrectly?