I know it is not scale looking but try adding some wingtips to it, my Avro Arrow was just stupid for roll and once I put wingtips on it you never would have thought it was the same plane. Can always cut them off if it doesn't work.
Awesome build, love jets but not EDF. I have 2 black spinners I want to use on a prop powered SR-71.
I think some winglets on the wing tip would not only set off the aesthetics, but cantered out a little will help with some stability. Possibly increase your dihedral if possible would definitely help, but this may complicate the build a little with spars etc.
Good luck keep designing, building and flying!