You need to do CATs throughout your prep, not just the last week.
Do practice questions on weeknights, making sure you're correcting mistakes when solving the problems untimed. Then do a full practice test each weekend, and compare the results. Are your errors the same type? If so, then work on fundamentals. If not, see where the discrepancy is.
It takes time to get used to the CAT format, and to hone your timing. Comfort level with the CAT is very important to doing well on test day, so don't wait until the last week to start your CATs.