Cut a length of crochet thread approximately 36 inches long. Insert one end in a large-eyed embroidery needle. Knot the other end of the thread. Insert the needle into the seam at the edge of the blanket. Take a small stitch on the seam to secure.
Measure 1/4 inch to the right of the knot and 1/4 inch in from the edge. Insert the needle at this point, from the top of the blanket to the back of the blanket.
Pull the thread to the back of the blanket. As you pull the thread through the blanket, it will begin to form a loop at the edge of the blanket. Insert the needle upward through the loop and pull the thread snug against the blanket's edge. This is a blanket stitch. The stitch is a backward "L" shape with the thread tail at the angled corner of the "L."
Measure to the right another 1/4 inch and 1/4 inch from the edge. Insert the needle from the top of the blanket to the back. Pull the thread through the blanket and insert the needle up through the loop. Pull the thread snug against the blanket's edge. Continue the blanket stitch around the blanket edge.