I finished the threading and the sleying. I tied up the shafts; I got my treadling pattern (an easy right to left and left to right).
I wove 8 picks of scrap yarn to spread the warp. Then I raised shuttles 2 and 5…and misery, no double weave. So I checked the tie up and saw the error! I retied the second treadle to be correct. The scrap yarn was taken out and I rewove it!
And voila! doubleweave! Two actual separate layers! I can see why one must check often the two layers.