Cut the top part off and fold in the fabric to the mark you made and going down at a slight angle. Iron the crease and pin along the edge. Then do the same to the other side. Now place the flat piece into the body of the bag, where it will be sewn later. Feel down to where the bag ends and the flap overlaps. Cut across about one inch below that point. Next take the flap and sew seams down along the pinned edges and cut off the excess fabric.