Your backing and wadding must be 3-4 inches larger than your quilt top on each of the 4 sides.
This is a total of 6-8 inches larger overall than your top on both the length and width measurements.
Please make sure that all four sides of the quilt top and backing are squared, straight and fully assembled. This is referred to as "Machine Ready".
No basting required.
When I lay your quilt top and backing out for mounting, they should appear as the above illustration.
For curved-edge quilts like Double Wedding Ring, the backing is still squared.
Remove selvedges before joining.
For pieced backs make sure fabrics are square before joining. I cannot guarantee center placement of the quilt top for double sided quilts.