I'm having the same problem, i can only access a part of the school from the side entrance (i think kitchen) and that lets me wander the final area where you fight with the elves, but im unable to get to places i really need to be to retrieve things, also unable to get into clydes house, or basically anywhere that has a chinpokemon or something to help add a friend, im super stressed as im a dire completionist and need to 100% this game. The game is bloody great though and ive had such a laugh playing it, not Laughed out Loud at a game in a long time, and Jimmy's (hold B to skip) stammer parts had me literally crying with laughter :'D.