Loft Petites S/M Sleeveless Peplum Top with Back Zipper

Ann Taylor Loft pretty maroonish-purple sleeveless peplum knit top with 13.5" back zipper Approx. 22" length (from top of shoulder), 17.25" pit to pit width Tag size is MP but measurements suggest this may fit like a SP? (See measurements) 72% polyester, 24% rayon, 4% Spandex (Stretchy & not too thin), machine wash & dry flat