I wear a medium too, and, if it shrinks a bit, that would be okay. The site says they run small, but they seem to run a bit big to me.
Also, to note: They print shirts only after the 3-day sales campaign concludes, so there will be a little delay before the printing starts. The items are on automatic three-day selling cycles or campaigns. But this is all explained on the store page and in the receipt you get.