No, no spiral. You should stitch left to right or right to left, whatever you prefer but not up and down. So start at the center and work that horizontal line for easy reference and counting. Then you can find the top left of that color and work that across. Don't do the height, just the width.

The baby blanket I'm making also says three, but I just find it so much easier to work with two that I just ignore their instructions :) I like two, I don't mind running the end of the stands under the back once I'm now, but I don't like holding the strands at the beginning at the back as I work over them, since there shouldn't be knots.