There's more than one level. Also, if you want mrdrnose to see things more quickly, go to Discord. See his comments below.
By the way, there aren't any exact hints as to where it is, but if you find it, it's likely you'll also come across something for an alternate ending to the Math Level. If you can open the door, it'll be in one of the lockers at the front. I just wish they stood out.