And what cost me most of the marks? My British steering technique: feeding the wheel through the hands rather than turning over the top of the wheel. That's correct for the British test, which considers crossing your arms at any time while steering a loss of full control (and risks an arm in the face if the airbag deploys mid-manoeuvre). But it's wrong on a Californian test: they consider the over-the-wheel technique to be more smoothly controlled.
I suspect it would have been less noticable in a car with power steering; the car I took the test in has manual steering and is a bear to wrestle around corners.
But it's over; it's done; I can drive legally and alone.