As others have said, I always try to fly the day before a check ride, and it does seem to help keep me sharp. Keep your composure even if you think you may have failed. During my oral, the examiner pounded my weakness (systems) with several questions. In flight I bounced (hard) on my soft field landing. The rest of the check ride was fine though and I passed. It is very difficult to fly a 100% perfect check ride, but if you know your stuff and are a safe, competent pilot the examiner will (often times) overlook a minor mistake.