Down a size?

So when I tried on my dress at the store, we thought a size 10 was the way to go. When the dress arrived at my house though, the dress definitely fit differently and was loose so I called the Jessica Mclintof store to see what they thought and they informed me that you can exchanged the dress for a different size all the way up to the date of the wedding as long as it is still in stock. Needless to say, mine was so they reordered it in the same size as well as a smaller size just encase the one that was sent to me was missized and I needed that size. Now just have to wait a while till it comes in to see if I am indeed lower in size which is always good!