Use the scissors to trim close to the pins. Remove one corner at a time, and pull one side of the batting, starting at the top corner, pulling the opposite side to overlap. Without letting the tension of the batting loosen, apply a little hot glue underneath the overlapping batting, along the corner, and work downward until the corner is glued in place. Trim the excess batting so it has a clean edge. Repeat for all four corners.
Trim the bottom edge about 1” longer than the cube. Set aside until you complete the cover.