It's nice to hear that you enjoyed yourself enough to play it twice.
The way that the map pieces work is that when you find all 3, the key is revealed. However currently the key is actually there and you can pick it up but it's just hidden. We discussed whether it should be able to be picked up while hidden and decided that it should, but perhaps that wasn't the right call.
Keep an eye out as we will continue releasing updates on Itch, and we're planning to set up a Steam page for the game soon!