Think of it like you declined the Full Collision Damage waiver on a rental car that you rented, had an accident, and then took the car back and asked the rental company if you can now add the insurance. Of course, they couldnt do it as its a insurance against what may happen and not after it happened.  It's advisable to add the insurance to your order it if you are unsure wheter or not you may have to cancel on short notice. Its already defaulted to be added so if you dont want it, you have to uncheck the check box.