The oars and things were still inside, which I discovered as I started digging with my bare fingers. It took over an hour, and incidentally the tide was creeping in, higher and higher, so it was a rush against time. I strategically dug the sand out in piles that would block the incoming tide. After I had most of the sand out I still couldn't budge the dinghy - it was stuck in the hole. I dug around it, my hands and finger now feeling raw and sore. It could rock the thing back and forth, but only after a big wave sent water to the edge of the dinghy, did I bring out the "mom whose baby is stuck under the car and lifts it" superpower, and got it upside down, draining water.
Soon I had the dinghy afloat and was rowing back to my boat, still sweaty from the exertion, way after midnight on a calm night.