Trim away the excess seam allowance on the wrong side of the garment. You do not need to remove the basting stitches from the leg openings. They will break when you wear the panties and will vanish by themselves. In the sample garment stretchy lace has been used to finish the waist. Baste along the inner edge of the lace around the waist.
Overlap lace ends leaving excess length.
Stretch the lace when basting. Using narrow zigzag stitch across the inner edge of the lace from right side through all layers. Trim away excess allowance on the wrong side of the garment. Using narrow zigzag stitch through the overlapped layers of lace. Follow motif if possible.