Aeronaut, you are correct.

For the purposes of the test you only get one shot at it (unless, as I've already said, because of cirrcumstances out of your control) of course "normally" you can keep trying until you get it right or run out fuel!
I believe the main reason for it is that if there's an emergancy (i.e full-size fly-by, technical problems with your plane etc etc), you have to land quickly, but in a safe controlled mannor - you won't have time to go around again and again.