It's true that if you take an AP Bio course that follows the AP Bio guidelines, you'll end up learning a lot more than you'll learn from FSc books. I have all the grades 11-12 FSc books and they don't go over every thing in nearly as much detail as most books you'll use if you're taking an AP course, since AP courses tend to use first year college texts.

The thing is though it's possible to score really high on the AP biology test without knowing a lot of detail. One reason is that it has a really big curve.

If you take your AP Bio course seriously and focus on everything your instructor requires (if you have a good/dedicated instructor), you'll have a much better understanding and knowledge base of the concepts than you would having just read FSc books.