I would dig into some of Stacey Koprince's old posts regarding this subject. It's certainly possible for people to get a lot of questions wrong on the test yet still end up with a top score.

My advice is to not worry about the algorithm or hit rates. Instead, focus on the questions you got wrong, analyze your weaknesses, and improve upon them. A lot of folks worry about details regarding GMAT scoring, but trust me it's not worth worrying about.

Good luck!

Everyone gets about half of the questions right and about half wrong, regardless of the score. This test is not scored the way we're used to tests being scored.

As Eric said, poke around and read some of the old posts on this topic - we've discussed this quite a bit.

But think of the test this way: it's trying to find the level at which you answer about half the questions right and half wrong - that's your score. NOT the level at which you get everything right. (Because, after all, that doesn't actually tell you much - if you can answer 100% of 500-level questions right, is that your score? Maybe you can also answer 100% of 600-level questions right? So this test instead looks for each person's "50/50" level, which varies according to the person's ability, to determine the score.)

Keep us posted.