I did CF for several months before my FF test years ago, scaled down most of the time. First time I think I got around 10 minutes (with a mild head cold), second time around I got around 8 minutes...if my memory serves me correctly. I did NO event-specific training. In fact, when they took my HR very soon after finishing, the guy was amazed that I was only at like 120bpm.
Just remember, the test is a pass/fail. If you already passed it and are now in better shape, you have nothing to worry about.
Worst thing you could do is train hard metcon stuff right up until the day of the event.