help with cgfns books , please

hi there, im a new user to this website, i ve been reading some of the forums which are very interesting. i am a rgn from UK
i am planning to take cgfns this year. i ve been using kaplan nclex book. is this book preperation enough to take cgfns exam or do i need to read more than that. i appreciate if anyone could please help suggest which books to go through. thank you.