Oh goodness - no wonder you're so disappointed - the piecing is so precise and neat, you must have worked hard on this.
I think the ones who've suggested tea-dying might be onto something.
You might also use white fabric paint with solid ¼" or ½" stars. Just mask off the areas you want to stamp and put the stars fairly close together. The areas in between them will still look pink from a distance, but the overall effect will be "white."
I hope you get some fun out of this, whatever way you go with it.