Laurie, kenkwan's right: if you're serious about quitting, you don't need to apologize. And you also don't have to figure out what to say during your meeting. You owe them nothing, and, if there's one thing I've learned, there is absolutely no point trying to explain to soon-to-be-former bosses what's wrong with the job: as a soon-to-be-ex-employee, your opinion is irrelevant to them.