Hi KB04,
I don’t think there is anything wrong with the GMAC practice test you took, and thus I wouldn’t waste another exam just to check. Remember, your GMAT score is based on not only the number of questions you answer correct/incorrect, but also the difficulty of those questions, among other things. So, at this point, rather than spending time worrying about the GMAC algorithm, you really should focus on the things you can control, and the number one thing you can control is getting better at the GMAT. If you get to a point at which you can dominate the GMAT, the specifics of the scoring algorithm won't matter because you will to have the skills that you need to get an amazing score, right?
If you have any further questions, feel free to reach out.
Good luck!!