I saw the film in the Easter holidays last year, but I've only recently read it.
The differences between the film and book are outstanding, for example in the film s*x is taboo while the book revolves around it. It's about this girl called B, who is matter of factly the unattractive one out of her friends - the duff. And the hunkiest, yummiest boy in her year tells her this.
This deals with a lot more than the film, this deals with family problems, self esteem and how to deal with it (good or bad) and just has so many themes which the films didnt portray. I understand why they didn't include it, because it wouldn't of been suitable and sent the wrong message out to impressionable girls.
But in this case the book is better.