PPI practice exam vs. diagnostic quizzes - which is more similar to the actual PE exam?

[studyingforthePE_10802]

I studied for a few weeks using the diagnostic quizzes in the PPI study plan and got at least a 70% on each section. Then I started the 2nd practice exam, and I'm 20 questions in, and I literally know how to do 0 of the questions. Has anyone taken the PE already or an NCEES practice exam & know why there is such a giant discrepancy between the PPI diagnostic quizzes and this practice exam? I don't think taking this practice exam is going to help me, it's just stressing me out.
Also, I know PPI is known for being more difficult than the actual PE exam, but I already paid for the study plan. Just wondering if my time is better spent on the diagnostic quizzes or practice exam