Cut two pieces of your fabric about 2.25 inches wide by 3 3/8 inches tall.
Draw a line with chalk from the top corner of the top piece to the side edge.
Cut the fabric off the top piece along the line.
Tie a knot in a long piece of 6 strand embroidery floss.
With wrong sides together start sewing a blanket stitch where the bottom of the new cut edge meets the back piece.
Begin on the inside to hide the knot.
Continue sewing along the edge down the right side, accros the bottom and up the left side until you reach the top left corner.
Tie a knot and hide it inside the cardholder.