The best way to fix this is to make a separate, second wall sprite and make that wall both a wall and a key. That way all the rest of your walls use the sprite that's only a wall. Hope that makes sense! Let me know if you need help.
No worries, it works now after copy-pasting your exact code into it... must have made some dumb mistake... lol. Thanks for your assistance! Great tutorial.
Just saw your other replies. Glad you got it working. It's possible wall and key were set to the same number in the code? Not sure. Well, feel free to reach out if you run into any other problems. Great work so far! :D The sprites look great and I love the premise of the game, haha.