U.S. History II Question

[sammy15]

I have gone through all the IC note cards. I received a 59 scaled score on the REA practice exam. I also took the "diagnostic exam" and even though I did better on that than the real practice exam, I ended up with a scaled score of 46. Does anything know why? Is it because the amount of questions on the diagnostic exam are fewer? I got 76 percent of the questions right on the diagnostic, compared to 65 on the practice exam. Thanks!