I love what you have done and it will look great as a center (like a medallion) on a large quilt. Just keep going the way you started and make each border, etc. larger. Blue border next to set the frame and then more of your pinks, and applique. Finish with blue binding.
If you measure your bed, then you will know where you need the zig zag rows and where to fill in with the applique.
Another border finish choice could be a "piano key" or "squares" with all the colors you have used in the zig zags and applique.
For what it's worth...just some ideas. I love what you have!!