Continue sewing your perimeter extension.
Working with the exact same process as you did to sew the wig cap, then work around your head stitching on the extensions that attach to the perimeter braid. Make each knot about 1-inch apart, and hold the extensions taut so that they are securely attached to a head. Do this all the way around your perimeter braid until you’ve made it to the very end, on the other side of your part.