i went through two entire semesters of A&P without a book! ... but that's just how the classes were set up at my school (the entire class had flashdrives full of powerpoints to take home & study instead of a book).
i definitely understand how reassuring it can be to crack the books ahead of time & see what you're up against, but like Asherah said, if the bookstore is backordered, then everyone else is probably in the same situation as you are. you'll be fine. good luck to you!