What does "doing terrible" mean to you? Does it mean not being first to finish? Does it mean not being in the year-end points standings? Does it mean not finishing the ride at all? Does it mean not having any fun?
There are lots of people who ride endurance to have fun and enjoy their horse and see new trails, so to them "terrible" would be not finishing or not having fun. While the really competitive people are racing, so doing "terrible" would be placing out of the top ten, etc.
A friend has done some endurance with her lovely TB gelding Kent. She is of the ride-and-have-fun variety, so never cared about placings but just having a fun ride. So def get your guy back in shape and see what you have!