I've completed the game (last level's name should be "Another Dollar Wasted", but both the title screen and end credits mention the game being a Demo.
I checked the version installed, and it's 1.5, the version that doesn't include "Demo" in the name. Was the demo version exported accidentally, or were the demo components not removed in the final version?
... Welp. That's embarrassing. Thank you for letting me know. The normal version just has a "The end" followed by the credits (which are also accessible from the settings menu) so you didn't miss any content.
Edit: Apparently the Steam version was even more borked. Thanks for pointing it out, I probably would have missed it otherwise.