First off let me just say, you are in no way alone!
I failed my NCLEX the first time I took it, pure nervousness!!!!!!!!!!!! I studied Kaplan and Lippincott the 1st time, which did not make or break me. Your comfort level has almost everything to do with the success of your exam. When I re-took my exam 3 mos later I went through the hospital, the nursing educators had an NCLEX review using Saunders. That was absolutely wonderful. I looked at the amt of time I had been out of school and reminded myself, we all have a learning curve. If we don't use it we loose it. Not to mention I did not want to review something I did not need to know. Kaplan is good, but it basically only teaches test taking skills. I would review Saunders and do the CD for simulated exams. Practice, practice, practice. Then, you will be somewhat prepared and have a better frame of mind. As far as when to take your exam, that lays squarely on your shoulders. Only you can decide if your ready. I had to go into the exam mad (because I let it beat me down the 1st time), determined, and with a plan (a break every 50 questions, or when my nerves could take no more).
I want to wish you luck and let you know your in my prayers!! You CAN do this. Before long it will be a distant memory! Keep your head high!
Sending positive thoughts your way!!!