Here is the completed spine, reinforced with ribbons, fabric, and craft paper.
I also made some wheat paste for the fabric covering.
2 tablespoons wheat flour
2/3 cup water
mix to combine then cook in a pan on the stove, mixing constantly, for ten minutes
Saving all those plastic containers is useful when you need a container for something like this.
Here's the book before covering. I had to cut new book board pieces since the first ones were a bit small.