In my opinion, feeling ready is crucial to doing well. Your mindset during the exam is paramount to scoring well. However, you need to realize that the longer you study the more likely you are to forget something (much like what you mentioned in your post.) If I were you, I would take some practice tests, see where I stand and see if I'm ready or not. If you do well, you clearly know your stuff and the confidence should follow.
Keep in mind, it's highly unlikely you'll ever know 100% of the material being thrown at you. Considering what most people use as their resources (DAT Destroyer, Achiever, etc...) learning all of it is just plain ol' overkill.
