It means, keeping the same number of rows in each colour (so your next row will be pink for six rows, then white for three, then yellow for three etc), and using the same stitch, crochet across 29 stitches. Turn as if you were at the end and crochet back. Keep going back and forth over these 29 stitches until measuring up the side you are working on is 17 1/2" from the bottom edge.

Thanks, Colleen. so I am really just extending the existing piece by 29 sts per row. That makes sense. I am also a bit confused about what is meant by "leaving remaining sts unworked". What does this mean?

Thanks again,

Cathy

No, you’re not extending, you’re starting the next row and crocheting across as you have been doing, but stopping and turning around and going back after doing 29 stitches instead of crocheting in (called “working”) the remaining stitches in the row.

So you’ll end up with a shape like a smaller square on top of a larger rectangle with the sides lined up on the right side, if you get my drift, where the taller side on the right is 17 1/2”, and where the smaller bit starts is where you stopped partway and went back the other way.

Oh I get it now...Thank you so much!

You're welcome!