What you did followed a clear idea, and you worked diligently enough to not distract from the idea. You traced the shape of the model with clean simple lines, adding contour lines to indicate volume. You abstracted a lot of details, like the specific clothes, the minute curvatures produced by fat tissues and muscles, and the lighting in the reference, to produce an abstract grid. Even if you wouldn't have underlayed it with the photograph, the grid you developed would give a very exact impression of one way a human body can relax, while laying back in a lazy or contemplative mood on a chair.
This is certainly a very valid way to simplify the reference you worked from.
I can't tell you whether you "nailed" it, as I am not entirely certain, whether you have a specific goal in mind going forward, but doing this exercise must have deepened your understanding about the human body. I have my own specific taste in how to develop a figure, and I watched and read enough explanations from other artists about their methods, so I could try to compare your approach to the reference to the way someone else might do it. I am just not certain, whether that would help or hinder you on your path.
TL;DR I find your result beautiful.
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