The NLN book generally has the information to prepare you for the exam. I did extremely well-above 90th percentile to be accepted in my program that I applied for.
The NLN does have time constraints, so keep in mind of practicing how many questions you can answer within a time period.
If you feel as though you need another book, look into finding another NLN book as well, it will only help.
If there are other nursing programs you are interested in, apply for them; keep you options open...you may score that 120, but still get on a waiting list. If you are a good candidate for other programs, apply to ones that you feel are a good fit for you; interview and go over their curriculums and potential preceptorships and electives.