Yep, that was definitely the most difficult bit. And because I was having trouble with it, I took my Dad's advice, too. Bad move. If I'd persisted I probably would have worked it out okay. But I listened to him and cut a little triangle off the end of one piece accordingly. And now there's a triangular bit there that had to be added in later, exactly the same size as the piece I was persuaded to cut off....
Kareela was canvassed with completely untreated cotton duck, straight off the roll. After completion the canvas was treated with a thinned coat of marine paint (it soaked straight in, and was a slow job), then with several coats of (unthinned) topcoat. The nett effect was to turn the canvas into a leather-like material, tough but flexible. (She was given a new coat every so often over the years, and is probably now a good deal heavier than when I built her 58 years ago.)
Mike