Worked on it some more at home - lots of rubbing out, and putting in more shapes with the help of the "templates" on the tracing paper. Useful tool, tracing paper. The drawing was getting very smudged - from a combination of the marks (soft pencil) on the back of the tracing paper, and using the quilting ruler "right side up" - the raised inking on the back was causing smearing. Even after erasing smudges - and especially after evaluating the placement of some of the elements - I wanted to start over, but sometimes Enough Is Enough. (Suddenly two hours had passed.)

Got those cubes at the bottom right, and figured out how to do "the underneath of the pyramid" (centre right). And you probably can't see it too well, but extra colour has been added - yellow and red at the top.