If I sew the binding on by machine, I do it just like you, except I use the sewing zigzag, which has the small stitches going up and down, not the big one stitch zigzag, instead of just a straight stitch. I fold the binding from the back to the front, and folt it just past the stitches from where you first sewed on the binding, and then I try to sew so that the zigzag comes as much exactly on the edge as possible, just to the edge of the binding and not unto the quilt part.