You didn't change the walls back into planes from combined meshes. When the decompile you used to make this was published most of the planes ("3D" objects with one side used to make the walls, ceilings, floors and doors) were made into unmovable combined meshes. Thus you actually just moved the collider, not the part we can actually see.
Viewing post in Baldi's Basics Minus (Legacy Versions) comments
Well, it's just that it looks like you can get through the hallway because there's no wall, but suddenly you're stopped by some invisible force field and you don't know which direction you can actually go. It's not really fair gameplay if there are random invisible barriers in the way, especially if you're not warned about it like it's a complimentary challenge. It's important to convert all the walls/floors/ceilings/doors to movable planes. Do that part in your original copy of BBIEAL 1.4.? from Jumpman, remove dark overstretched planes that you got and maybe recreate the dark hall that used to be there but got spoiled by the conversion to plane. Then save the project, export a unitypackage and use that modified prototype for your next decompiles to prevent any confusion or neglect. Should do the same for the Secret scene as for the School scene.