Cute multi color blue Plaid shirt by SO, Says size M..It should say XS!

Cute lightweight plaid shirt has 3/ 4 sleeves that button up. The shirt is by SO (brand by Kohls). Says it is a size medium. I tried it on, and I'm a size 2, give or take. I couldn't get my arms through the sleeves. I would call it an extra small. Also,it probably would fit children under twelve. The blue colors are very fun and it will look very cute paired with jeans or denim shorts! Never worn, just stored. Is 100% cotton, Not flannel, so it's very lightweight.