Sew both pieces B on the sides of piece C. If you want to enclose your label, do it now. Iron your seam open.
Sew along both sides of the seam.
Place piece B/C with the right side up. Sew your ribbon on the side that will be on the back of your notebook. Be sure to stay within in reach of the seam allowance. Then place both pieces A with the seam on the inside on top op piece B/C.
Place piece I, your lining fabric, with the wrong side up on the rest of your fabric. Sew 0.5 cm from the edge and leave a small opening on one side. (Be sure to do it way more neat than the line I draw with my mouse) Pull the inside out and ladder stitch the opening. (This is another piece of fabric than I used in the end. I forgot to take a picture of that one...)