I agree with the above post. DO NOT use chinagraph on the old whiz wheel, a pencil will be much better at doing the trick! Also, re-check when doing the planning stage before going onto answer the questions. As you said, if your planning is wrong/inaccurate then your answers will follow the same path! Just take your time and don't rush. I'd recommend a good 20-30 minutes planning before attempting the questions.
I'm sure your instructor will be willing to offer advice. Hope the next one is a pass! Good luck!