Is this an old quilt? It appears someone has replaced two pieces with a similar fabric. If you can find some of the original fabric, then the repair that would please you most is to open the quilt and replace those two hexagons. If you don't want to go to all that trouble, then I don't see how you can hide the zig zag stitches. Perhaps "applique" some new hexagons over the zig zag ones.