Nice, this is a good start!
When you tell the player to press O to open the door, you need to press O at that time when that message is on screen - if you press enter instead, to end the dialogue box, you can no longer open the door!
I can see why this would be missed by the developer - you already know how to play the game, so you know to press O right away, and didnt think people would do something else. This is a good example why you need to have other people playtest your game! Its very easy to miss this sort of thing.