Lift the square layers away from the rectangles. Place another set of two rectangles on the square side adjacent to the side you just sewed; make sure the rectangle you want to show on the outside is facing out.
Align the square edges with the short sides of the rectangles; pin. Following the same sewing directions above, sew the four layers together.
Repeat the same sewing steps on the other two sides of the square. Your basket should now have four sides.