Hi santo
The highlight's looked fine, where you've upped it, it's washing out the image now, so go back to where you was with the highlight. It's mainly the shading under the fuselage, especially the engine cowling its' very oval shaped on the real thing so the darker shading at the bottom needs to progress more up towards the centre line of the aircraft. I've found some cross sections on the net (dunno how accurate but should be ok'ish).

Basically the dark fuselage shading should fade from the bottom of the fuselage gradually getting lighter all the way upto where I've drawn the red line on the cross sections. This red line is where the fuselage starts to curve under so therefore from the red line the underside shading should gradually start to get darker.
Hope this helps?
Clint