Please check the maps
and the video
and see if it helps.
As you had an error in your game, check if the last key is in your inventory. If not, go back and get it again.
If you have done everything exactly like in maps and video and it still does not work, you will need pixel support.
I will remove the bug report for now. If pixel support has to fix your game because it is indeed a bug, please report that here, then I will put that tag back.
Hopefully maps and video will be sufficient to help you out.