This is corrected for Verison 1D and above.
Corrected:
Rnd 3: Ch 1, 2 sc in first sc, sc in next 7 sc, 3 sc in next st, pm in center of 3-sc group just made to mark corner, sc in next 7 sts, 2 sc in last sc, turn––21 sc
Incorrect:
Rnd 3: Ch 1, 2 sc in first sc, sc in next 6 sc, 3 sc in next st, pm in center of 3-sc group just made to mark corner, sc in next 6 sts, 2 sc in last sc, turn––21 sc