This is a closeup of the spine with the fabric glued on. All the gaps between the score marks get glued to the fabric and that is the strength. I place the glued spine on a teflon craft sheet so it doesn't stick. I leave it to dry overnight, standing on its edge so it sticks. The book is now finished if you want or you can add decorative stitching for added strength.
This type of hinge without card along the spine means your book will open flat no matter where the page is in the book. Have fun with this and use whatever supplies you have on hand. If you make a book leave a link in the comment section so we can all see your wonderful work.