That's really unfortunate.
I'm not sure how useful this would be. but one thing you can do for your next practical test is to inform the instructor of what you're about to do. During my exam when there was situations that could have resulted in an alternative decision, such as overtaking a bus. I just said, I can't really see behind the bus and further down the road so I don't really think I should over take in this situation.
I think if I was in a scenario similar to the one described in your situation, I might say something along the lines of, I'm just going to budge forward a little or creep forward a little to make some space.