Adam,
The main issue here is that the paint finish on a car is reflective (as you realise

). Your work so far removes the existing reflections, but doesn't replace them with something else. Hence your car looks like it's painted with matt paint

Look at the original. The bonnet reflects the windscreen, the illuminated roof of the tunnel, the lights of the roof etc. You need to create new reflections which are *believable* in that situation. At the moment you have none. Hence it doesn't look real.