I was taught to do two rows of basting (similar to this method), for gathering. Pin each end, to seam line. Then fold to center of ruffle, matching center of seam line. Pin. Then fold to center of each piece, between pins. Match and pin. Depending upon the expanse to be sewn, this may be done several more times, before adjusting ruffles and sewing together. Been sewing over 50 years.