So you fluffed the reverse, all part off the job, we all have bad days.
The key is to learn from it and move on. You otherwise passed your test, 4 minors is a good result and shows you have it in there. Needing a bit more practice on the reversing is a very common problem with new and experienced drivers. At least it was in a test centre environment and not on the job. Keep your chin up, don’t lose faith and go to that next test rain or shine with the right level of confidence and you will pass.
Then the real learning begins …
Good luck