Not finishing an order/giving the wrong order will not result in a jumpscare, so don't worry! The customer will just leave and the timer will go down! In order to get to the dungeon, you need to complete the baking mode! After that, to go through the dungeon, you'll have to collect the notes scattered throughout the map and type in the code you decipher from them at the keypad next to the door! They always spawn in the same location, but the code is randomly generated each time, so if you get caught, you'll need to collect all of the notes again! Best of luck!