Step 5: Add the drawstring
Sew a second seam around, 3/8" out from the first seam, being careful to keep this same distance all the way around. Now you have a channel for your drawstring. (The first picture in this step illustrates the two new seams in black but, again, use bobbin thread and spool thread the match the two sides of your bag).
Cut a small slit in the outside fabric only, between the two seams. Cut another slit in the outside fabric only, between the two seams, but on the opposite side of the large circle.
With needle and thread, reinforce the edges of the hole with a whip stitch. Repeat for other hole.
Catch one end of the ribbon or chord (drawstring) in a safety pin and insert into one of the holes. Use the safety pin to push the chord through the channel, all the way around (ignore the other hole when you get to it, just go right past it). Tie the ends together in a simple knot. Repeat with the other chord starting in the other hole.