Notes
Garmin says 20.88km, not 21.1, but I'm going to claim the HM distance. The hills certainly added to the task.
I'm guessing the official distance was based on staying one one side of the road & I took the tangents.
Felt fairly good most of the way, and recovered quickly after a brief flop on the grass.
Measured intervals at the official 10k, 20k, and finish.