That is so wrong I assume you didn't buy a discounted dress? If not, before your dressmaker fixes the problems, I would ask her to take photos. Then you can send them to the store, and ask for a discount, based on the dresses condition. If you're not happy with the stores response, let them know you will be contacting Consumer Protection, and showing them the photos.

It may seem a lot of effort this close to your wedding, but you shouldn't be out of pocket for faults that weren't caused by you, KWIM? GL hun