I did my prep exclusively with Kaplan materials, and my Kaplan practice test score was lower than my Powerprep 1 < Powerprep 2 < Test Day.
Kaplan materials are sometimes difficult, but I personally feel that they are a great start. Focus on your process. When you get something wrong, don't just look at the answer and say "Oh I see. ok." This is a terrible mistake many people make, which can result in months of prep leading to little benefit. Think about how you can tweak your process to get something like it correct next time!
And for the record, I'm a mathie geek who hated English, but got 99th percentile in Verbal.
So... think about that 30% as an opportunity to get even stronger!
