I shortcut leaving 3 inches all around a queen size quilt once and thought I could keep it from shifting as I stabilized it by STID around the blocks. In the end one end shifted back about 1.5 inches and I had to piece in a section of batting and a section of backing. This was far more trouble than if I had left the proper perimeter to start with. When I completed my repair job an onlooker could not see it but it was sure a lot of extra work. It will never happen to me again. Be safe and use a bit of a safety margin and use the scrap for a scrap quilt.