I am confused by why you unpin the bottom of your quilt. When I load my quilt I pin the backing to both the upper and lower leaders with the backing being several inches longer than the quilt top. Then I pin the bottom of my quilt to the lower leader, roll it up and float the top edge close to the upper leader. I pull the batting up between the backing and top. I baste the top edge of the top and batting to the backing and then proceed on to do the quilting. It is also good to baste the sides of the top as you move down the quilt. You always need to have extra backing in the length as the quilting uses up extra fabric.