Demons don't always deal with Satanism per se. Demons are basically spirits of lower ethereal origin. The aren't all evil nor are they all looking to mess up your life just for kicks. In my experience there's little you could offer one within his interests. If you just want to get into college I don't see why you can't just try talking to one, but again there's little interest they typically have in humans so winning their audience might be a moot goal.
There are practices though dealing with certain demons or demons in a certain manner that may pose danger but they aren't necessary in this case nor are they meant for such a simplistic, and rather earthbound scenario as getting into college.
My advice is to forget about the demon deal thing and think of a more practical way to get into school.