I would just keep my zig zag stitches open and loose. The more stitching there is, the more the fabric draws up. So I wouldn't use a satin stitch at this point.
Another idea: make the flower petals individually so they are double sided and "birthed", the same way you stitch almost completely around something then turn it inside out. The arrange the flower petals and attach them with embroidery thread and french knots at the centers, allowing the petals to be loose.