I'm so sorry for the late response!! I don't usually check itch T_T
I'm not sure if you've already solved your problem, but just in case: make sure you've deleted any older versions of the game!! There should be a "Ren'Py" folder somewhere in your documents/applications folder; and inside it should be a "14 Days With You" folder as well. Just delete (or move) the entire folder and see if that works! If not, you might've downloaded the wrong file ^^;