Ralph Lauren Purple Sequin Dress (size 10) but feels like 6-8 sz for party prom

Purple sequin top dress, brand new, never worn, with tags. It has a metal decoration on the left side with a few ruffles. See pictures. Size 10 but I am usually a 8 and it feels tight. 15 inches across tummy, 16 across chest, 24.5 inches skirt length. Zipper at the back. Great condition. No rips not stains. Never worn.