You can most definitely get multiple endings in the game, are you sure that you've explored everything? I can clue you in in case you are still interested.
cant say I ever got to a game over or game won screen, like I did what was visibly doable for me and the unfinished stuff (other side, island of whatever) seems to be the only thing left.
will go around the game once again though, still have that graveyard key that I dont know the correponding graveyard to :-)