Unfortunately nerves play a big part in how people feel when they take their test and can impact on a persons performance - it is important to feel confident in your ability and not to take your test until you are ready. When your instructor says that they feel you are ready, believe in their opinion and believe in yourself. They would not let you take your test if they did not believe that you were ready.
Its important to go out near the test and calm your nerves.
Try techniques to calm your nerves around the days before the test.
Have a good meal, make sure you are hydrated, had a good night sleep, feel alert and focused.
If the examiner is not very chatty - talk to yourself to avoid your mind wondering off in a pattern of worry. You could become an instructor inside your head - look back to your first lesson - think of the amount of information you were given to perform tasks - use this information to guide you so that you cover all the areas required to pass your test.
To summarise - believe in yourself, don't expect, be determined, prove to the examiner that you can do it, that you are a safe, competent and independent driver.