Pin the 4th corner and the first few inches of the side. For the final blanket edge, cut the satin so that it overlaps with the beginning plus 4ish inches. Do the same airplane-wing fold as in Step 6. Iron so that the new folds are on top of each other.
Finish pinning the satin around the blanket edge taking care to make sure that the tip of the satin is even with the edge of the blanket. Sew the corner as in the previous step and use zz2 on most of the rest of this side. Just before the tip of the satin, use zz1 (back and forth) to secure.