Your quilt is beautiful! How much larger would you like to make it? Do you have enough of the green and red to do a 9-patch all the way around, I think that always looks good. then maybe a border of the white. That would make it quite a bit bigger. Stitch in the ditch is always a good way to start, it stablizes the quilt, so you can go on and do fancier things. MAy be stippling or crosshatching, even jump in with all feet and try feathers. What ever you do it will be beautiful.