Yessica plaid button down shirt

Yessica at C & A plaid button down blue, white, and green top with adjustable sleeves and front pockets. Good condition. 100% cotton. From Germany, my sister in law bought it overseas. I don’t fully understand the sizing comparison chart for this top, my research says it should be an XL, but when I try it on, I can fit in it, but it’s a tad tight/small. I consider myself between a small and medium, so therefore that is why I’m listing this piece as a small. If you know better than I, please give me insight! Or feel free to ask questions.