The confusion is understandable, I can totally relate to that. As you can see in my post above (in which I mentioned all my scores), my practice scores were very low as well. The last test I attempted was PowerPrep V2.0 and got a shocking and worrying 147 in the Verbal section! However, a week later I got a 157 (73%) on my official test. And keeping in mind that I'm not a native English speaker, I'm really pleased with my score.
From my experience, practice tests are not exactly the best predictors, especially unofficial ones (like Princeton, Kaplan, Barron's etc.) that are not at the same difficulty level as the actual test. So, no need to worry. Just keep up the hard work and it will pay off for sure.