When I have the foundation telephone paper completely covered with strips, with at least a quarter inch on each side I trim the sides. You want to place the fabric piece upside down on your mat so the paper is showing. Then cut the excess off. Place your ruler on the on the foundation paper hanging over the side a quarter inch and cut. Do this to all four sides and you will have a square that looks like this pictured here.
front
[ATTACH=CONFIG]177104[/ATTACH]
back
[ATTACH=CONFIG]177105[/ATTACH]
trimmed back
[ATTACH=CONFIG]177106[/ATTACH]