Charcoal formal boutique dress

Black sleeveless dress with high neck collar. Has belt around waist, open lower back, and poufy bottom. Material is polyester, nylon, and Elasthane. It's beautiful and looks like Audrey Hepburn's style. Bought it in Vegas at a boutique but immediately had buyer's remorse. Went back the next day to return it but the boutique didn't accept returns. Unfortunately, now it does not fit. This dress has never been worn so it's in perfect condition and still has the tags on it. It looks amazing on!