I took the ARCO Gold test recently (which is great by the way) and I got around 60% of the questions right but I ended up with a 90+% percentile score on the verbal. When I looked at the distribution things began to make some sense. I don't remember the exact break down, but I got the first 10+ right (it might have been the first 12-15, I don't remember). On the other hand on the math section I got a much greater percentage of questions correct, but I missed some questions in the beginning of the test so my percentile score was actually lower than the verbal.
I believe it is possible to miss a few beginning questions and still get a good score, but if you ace the 1st group of questions your score should be much higher. That said if you miss early questions AND some later ones you wont score that well.
Oh, and don't get hung up on the "level of difficulty" of the problem. If you get a question that you feel is really easy on question 34 don't freak out. It could be an experimental question or maybe just a question that you think is easy but others think is hard. Just take on each question 1 by 1.
Best of luck!!!