Hello sweetie,
I'm making one of these for my grandaughter. Here's what you do.
First decide how wide and how long you want it to be. You are working with 6 1/2" blocks and once sewn THEY BECOME 5 1//2" blocks because you want to have a 1/2" seam allowance on each side for fraying. I would suggest that you put blocks of flannel in between, like a sandwich to give it more warmth, softness and durability. You could also put flannel on the back also and you would have a really sweet quilt. You could use pink and white flannel for the back which would look real cute with your fabric.
Any way, 10 blocks across would be 55 "
13 blocks down would be 71-1/2 "
You need 130 block for the top, 130 for middle, 130 for back
Don't let that overwhelm you because you will be using three at a time. You daughter can help you layer them for sewing. If you have someone doing that it will go fast. Good luck.
If I can be of any help, let me know.
Cheryl