I fiddled with it and was able to get it to lock. REALLY took a good WHACK! on the gas cap. Using the key worked to open it.
I wonder why Honda used a fake lock to close it. I mean if they were looking for a better latch design, they could have gone with a conventional turn latch instead of one pretending to be a lock. Maybe to discourage would-be gas thieves? It was after the oil "crisis" in '73.