Yeah that's the ending. As I made this game in 10 days I didn't really have time to do much better unfortunately. Glad to hear you got lots of play time out of it though ;P. I'm currently working on a small update which will add a few more places to visit, improve the ending, and fill out the story a bit better. That will probably be released in the next few days, but until then that's the full extent of the game.
Edit: Currently you have no access to the master key( it is basically just a "Door is jammed" substitute) However I do plan on adding a "Master key mode" unlocked by fully exploring the game and reading all the notes.