Baci Lingerie School Girl Set

This is a white halter-neck tie-front top with a navy, green, and red tartan pleated mini-skirt. The skirt is stretchy and has a zipper at the back. The label states it is a OS (one size fits most) but it is better as a size small or medium on the smaller side. I tried it on once. I am a medium on the bigger side so it doesn't fit me the way I would like. I am open to reasonable offers.