So, fortunately I found a yard more of the same line Mixed Bag by Moda on Fabric.com and its on its way here.
My plan for the back was just piece it. I took some scraps, sewed them together, squared them up and then added another piece.
Here you can see I chained pieced these similar sized scraps together.
Then I did the same with some larger scraps.
After squareing them up I fit pieces together I. A way that I thought they would fit together. I didn't really pay attention to the pattern on the fabric. I focused mostly on the size.
I'm learning as I go here, so this photo isn't very good at showing what I am doing. But, I have one long piece of fabric and a shorter piece. I guessed at about how much fabric of the other piece I neede to add to make hem roughly even. I had some 2" strips that I sewed together to make a little block to fill in the space.
It was after this last piecing that I ran out of fabric. Now I have to wait for the additional fabric to arrive so I can finish.