I believe if you had a previous reservation you'd have to cancel it and rebook under this discount code. You could split it up so that the 2nd half would have the dining. They don't automatically give you free dining without booking the discount.
I'd give them a call and see what they can do for you. Based on availability at that current discount code they may be able to modify your original reservation from 10-13th, then rebook you from 13-15 at the discount. I'd call ASAP before its gone!