momoftwo. If your curtains are delivered to a Jcpenney store you can ask them if you can still apply the the coupon for friends or family, or the free shipping code after you placed the order.
Most stores are willing to make adjustments then having you cancel the order and reorder the same items again.
Momoftwo. Your second part of the question was: can this be applied to the free shipping too?
Generally, you cannot double stack coupons.
But if your curtains were sold in the JcPenney store the store associate could of ordered you the curtains at the store price, then had them delivered to the store with free shipping .