Some years since mine, but a thought or three...
(1) Relax and try and enjoy it
(2) Just do everything exactly as you've been taught: neither more nor less.
(3) You won't fail for making mistakes, unless they are massive howlers. The way to fail is to not spot and correct your mistakes in a timely manner.
(4) After you've passed - and remember that your instructor wouldn't put you forward unless he or she believes that you will, remember that the PPL skills test is the lowest standard you want to show afterwards, not the highest. Try and treat it as the start point for improvement in years to come.
G