What a pretty quilt for a child! I'd ask the person who donated it if she still has any of the rest of the fabric. Hopefully she does!! Then I'd complete that as a square quilt and donate it to a spot that needs cheerful quilts for kids--even an adult care facility needs cheerful colors.You could salvage a few of the border blocks by taking one row off to use to come on around but finishing that inside square? Could you introduce another color to alternate some blocks to stretch what you have there? I think you can do this!
Let us see what you decide to do.