I wouldn't worry too much. I used Crack DAT Reading as well. I was scoring right around 17 on most of them and I got a 22 on the reading section of the real thing. I thought the passages were easier overall on the real test (except for test 1 on CDR...I remember that one being exceptionally easy), and I found it MUCH EASIER to search and destroy on the real test. I recall there being too many tone/inference/interpretation type questions in CDR.
That being said, I still thought CDR was a good way to prepare. It will help you get your timing down, and like anything, the more you practice the more comfortable with it you will become. Hope that helps.