I have seen 2 other developers here posting the same game! Some stuff are not the same in those builds but it is the same game! I am not even sure if you are the original game developer of this game, kinda hard to tell when such things happen (Can't remember the other game pages' names)
Anyways! In all the 3 different builds of this game that I have tried, I could not find the 3rd key to open the door, where is it?