Wouldnt worry, reversing is its own artform and you’ll get good and bad days even years later.
What you have to remember is the back of the trailer is a long way from you, so it takes a while for your requests to translate into actions…bit like turning a large ship. Then of course it takes ages to stop those actions.
Little and often is a good stratergy and take it slow too. The reverse on the test is nothing like the real world and it would help if we were taught why we wrre turning this and that way rather than memorising a series of moves.
I remember my first real world supposed 90 degree reverse - think dog chasing its tail backwards and you get the picture of what actually happened. 
Have fun with it!