I believe the PTS uses the phrase "continually exceeding tolerances" to describe a failure. Nobody's perfect. If you make a mistake, FIX IT. Don't just assume you're dead in the water. I gotta agree with Mike. On my initial part 135 PIC checkride, I set up a GPS approach. I began to fly the heading that the GPS said to the initial approach fix. I was continually re-analyzing how things were going. I noticed that the heading didn't seem to make sense. Ok, time to do something different. I wasn't busted because I took steps to correct my mistake. The check airman said that he doesn't mind when people make mistakes if they figure it out and correct it. It shows that you are capable when you can fix your own mistakes without being prompted. Good luck. The best thing to do is relax and not forget that you are the PIC and the examiner is just a knowledgeable passenger.