The plot of the book is basically: should Sam have sex with her boyfriend(who looks suspiciously "hot" on that cover- good luck finding a sixteen year old who looks like that)? That is the sole plotline- the book is nothing more than Cabot's political views on sex, which she is very pushy with. Completely irresponsible, bearing in mind that her readers will be younger than sixteen and may even be as young as twelve, considering the simplistic style of her writing.
I'm sure that the plotline could have been dealt with in a mature way but Sam comes off as surprisingly immature even for a sixteen-year-old, so her transformation at the end is completely implausible. I'm not sure that the masturbation tip was particularly helpful either- just get yourself under a running tap for a practice run and away you go! Seriously.
In a world already sex-obsessed, this does nothing to dispel the myth that every teenager should be obsessing about sex, and if you aren't having it, you're "uptight" or "not cool".