Regarding the exit: After I posted last night I decided to simply add an explicit “continue” button, unconnected to the backdrop door (save for also being at the bottom-right of the screen), which should remain on-screen even when the window-size bug takes effect.
I’ve updated the p3d, and you should be able to download it using the link in the first post. 
I’m glad that you mentioned that–thank you!
Indeed, this minigame was originally created, as I recall, as an example game for the key-mapping system that it uses.
(In fact, if I may confess, I intentionally made the default bindings a little awkward in order to encourage players to use the key-binding interface.)