It does not have to be perfect in anyway shape or form but it DOES have to be safe.
Mine was far from pretty at times but if something is not right do something about it i.e. too high, too low, too fast, too slow, off track etc. Recognising something isn't right and correcting it is often just as good as getting it perfect.
Unless you do something totally daft I'd say the only way you would fail is if the instructor has to take the controls for reasons of safety. If you failed for any other reason you weren't ready for the test.
Above all examiners want you to pass and work with you within reason and the concept of a test environment to make that happen.
Are you sitting your test in ABZ?