I'd have to agree with Tracy. Her solution sounds like it needs a bit of a preview to be sure that is the right one that you will be happy with. But on the right track. That kind of border will enhance the center and balance the quilt. It will not take away from the zinnias. You want to have eye movement across the entire surface of the quilt to add interest. I just made the mistake of having a rather bold, vibrant center to a lap quilt and quieted the borders, too much. The center pops too much. That is the danger of a very plain border. Beautiful work you have done already. Please post the finished piece!