Whilst I can see that only really focusing on the test reverse has its merits for clarity, I do agree all proactive is good. But the OP hasn’t got that now as the trainer has let them down. 
So my advice is find a friendly co driver and blag a bit of ANY type of reversing practice. I had to really focus on which way to turn the wheel when I started, and the more practice I got, the more natural it became…
As for tips beyond that, come back once you’ve done a bit and ask again! 
Best of luck.