This is a story based achievement and cannot be missed. After beating the boss in the first room of Wonderland (After turning on the lights in the room through the tea garden), you will lock the keyhole in the doorknob's mouth. The achievement didn't pop for me, however, until I used the save spot to board the gummi ship.
Here's a video guide if you need one. I did not create it, all credits on the video go to its creator!