Standards document 03 tells you all you need to know.
Torerances are 'minimum' standards, you should aim to stay well within. Examiners usually brief that straying from the tolerances does not result in immediate failure, provided you make a smooth correction as soon as possible. i.e. don't spill the Gin and Tonic.
If you do anything dangerous or illegal during the test you will fail the relevant section. If you make a mistake, not necessarily, it depends on how you rectify it. The CPL is all about CAPTAINCY and AIRMANSHIP.
Advice for the course itself:
Listen to your instructor, ask lots of questions, back-seat as many flights as you can. Chair fly frequently. Know the aeroplane by heart, know all the emergency drills by heart, and the speeds, read the POH thoroughly, know what every single button and switch does, and how to operate it properly. Prepare nav flights thoroughly, and as far ahead as possible - have a plan A, B, and C. (I have seen people fall apart spectacularly when plan A fails, because they never thought what if??). Listen to the examiners briefing, and ask questions. Make a good first impression. Don't 'brain dump' all your ATPL knowledge, especially the regulations, M&B and performance stuff. The examiner wants you to treat him like a fare paying passenger.
Good luck.