Julian and FFF are quite right, as usual. One more tip... If you mess something up, speak up and say that you know you have got it wrong and tell him what you are going to do to fix it. Better than trying to hide it (they'll have noticed)
I was really nervous before my test, but once in the air I relaxed - too much - and was so busy enjoying flying that I was almost into Farnborough MATZ before I realized that I had forgotten to talk to them. ******. I confessed to the examiner that I'd screwed up, told him what I was going to do (orbit while I talked to them and got the MATZ crossing) and got on with it. Passed OK. Obviously if you've just busted the London TMA then you'll fail, but if you catch it in time then there's hope.