You may be having a problem lining them up. You want to finger press a center mark on the triangle and the square. Line up those marks, pin and sew. Do the opposite sides and then press. Then do the other 2 sides. Again finger press and line up. Once you are more experienced, you will be able to eyeball how they line up, but until then, the finger pressing will help with the little 'hanging ends'. And, as we tell all our students (quilting and sewing), the iron is almost as important as the sewing machine!