Jo

Personally I wouldnt book a test until you're feeling confident in the car. Chances are you'll fail, then feel even lower.

Try not to take the criticism as negative. if hes repeating himself, then its frustrating for him too. Time in a car is the answer, just keep working at it.

It'll come eventually

EDIT:

Try booking 2 hours slots if you can. That way you'll get into a rhythm after 30 mins and still have a hour or so left to practise.