mate I have been there two months ago.
failed the first test on reversing excercise. Did it perfectly on the retest with just one shunt.
Driving at work is different though. I do Still need few shunts from time to time - although some tight places I am able to do it without them.
Here is what I did - bought myself a driving wheel, got Euro Truck Simulator and practiced for about half an hour daily. It did help.