Twin stitch, starting at bottom hem, stitching up to the notch, and continuing just 1cm(3/8") past the notch. Pivot here, leaving twin needle down in the fabric, lifting presser foot and turning fabric. Stitch approx 1cm(3/8") across, pivot again and stitch to bottom hem on other side. (Yes, it is possible to pivot a twin needle - it may appear a little bunched up to start with, but smooths out afterwards.)