Agreed. Though be careful - nothing is "for sure". PowerPrep can be skewed high if you use the OG to study, cause some of the questions repeat. Scores have a natural variance on any given day depending on your level. And nothing can tell you in advance exactly what you will score, how you'll deal with test-day stress, or what specific questions you'll face.
Practice tests can give you an idea of what you'll score, sure. But don't rely on them too much. You're in danger of being over-confident if you score high, or being depressed and nervous if you score low.
CATs are much more useful as a diagnostic tool to find out what
areas of weakness require extra review. They're also useful to build stamina and practice under test conditions.
Don't worry about the scores so much. Focus on understanding the questions - those you got right as well as those you got wrong.