Matte Satin has no stretch. It cannot be let-out without damage. If you're between sizes, you may want to size up from your typical size. It's much easier to take in a Matte Satin dress.
The natural waist and bust measurement take priority in this style. If you are over by an inch or two on the hip, you should have enough room to release the side seams to allow for that variance. There will be a bit of ease in the bust as well.