I saw a tutorial not to long ago that suggested ironing your backing so you had creased it in 1/4's. understand?
do the same with your top. then you tape a cross of wooden dowels on the center of your table. do what you can to mark the batting in 1/4's also. then you feel the wooden dowels thru the center of the backing. then she taped, or used large clips to fasten the backing to the table. next the batting, then the top. lining up the center 1/4 creased lines. follow the creases out to the edge. I had thought at the time, that this would work for a biginning quilter to get the hang of laying out the sandwich.