System 7,
Not to disrespect sfoskn, but I think if you are aiming for a 20 AA then you might just be ok. If you believe you are ready, and you have covered every single thing in kaplan BB, then you should consider taking the exam. A problem with alot of students is that they take mock exams to see how they are doing, where as the grading on the DAT is a lot different from these mock exams. Instead I suggest you use these mock tests to improve your timing, and to learn things you may have not learned. Simply take the exams as if you were taking the DAT, then sit down and go over every question (including the ones you got correct).
If you are aiming for a higher grade than a 20 however, I do suggest you reschedule until you are confident in your self.
hope that helps