Hi and welcome.
This is a common complaint with white or light gray paint schemes.
For starters, try adding some shading effects on the leading edge of the wings. Notice how the original wing art is slightly darker on the front edge? Give that a try, as this will help improve the 3D effect where the lighting is actually more flat. You can also add these kinds of shadow effects under the exhausts, the machine gun mounts, and the struts on the wings.
That should be a good start. Just use a subtle feathered brush, and build up your shading on a new layer, so you can vary the transparency of that new layer to adjust the amount of shading, without having to repaint if you want slightly more or less.