I understand that you only get one shot at each manuver? so if i have an engine bobble mid way thru the overhead eight (assuming i get that far:}) then that is it for that manuver, don't get to do a few level laps then try again, right?
You're right. You get one shot.
The judges are going to look for each maneuver in order. Trying again disrupts that order. If you deviate from that order, they will be thrown into chaos and have every right to score every following maneuver as a 10. There has been an understanding for many years, however, that after you've completed all but the landing, if your engine is running long, that you can pull some tight loops or something to kill the engine. Keep in mind that you'd best have at least two level laps after the last flying maneuver before you try that.