When I started reading this book I actually thought it was plausibly a real diary. I grew more skeptical while reading it, but thought maybe just possibly someone could be dumb enough to write a few of the things that were making me doubt. So when I finished the book and then looked at some reviews online it was not a shock to see that it was fiction. It made me think of how the movie Fargo claims at the beginning that it is a true story. And I also recall someone saying that the producers of Fargo admitted in an interview or something that of course it is not a true story but that making that claim at the beginning is a powerful device to suck the viewer in.
That device did positively affect my enjoyment of the book.
My main take-away from the book is that the parents really failed. Letting your child go to a party without verifying the circumstances of it is pretty whack. Of course this is coming from the guy who did not go to parties in high school so...whatever. But the whole plot in my mind hinges on the parents being idiots.