Women’s summer jumper

Brand new women’s summer jumper very very cute. It’s a size medium too small for me. It is a total of 18 inches from under arm to under arm across the back, wide leg doesn’t fit so cute 15”, under breast around the rib cage is about 16”, I am really bummed that this does not fit. It’s just a little snug around my rib cage and plus I can’t zip it up myself.