(A) Fold extra skirt fabric over the folded back corner of bodice. (The flap formed now has the right side of skirt on top of wrong side of bodice.) Re-pin this section through all layers.
(B) Fold edge of skirt back 1cm(3/8") and pin in place.
(C)Sew through all layers, ensuring straps are not caught up in this stitching.
(D) Zigzag/serge this seam to finish it.
Turn flap right side out.