nice chop,
imo dont be that bothered about refs , lighting is way more important ..
the cars paint is way to bright and saturated , where the bg is dark and the sun is seen true the trees so the side of the car we see should not have those waaay bright hightlights / lighting
so that said you should have used a different bg with totaly different lighting
i always say find a bg that fits the cars brightness / lighting rather than the new bg looking cool
most important is the fact if the car fits into a new bg or the new bg fits into the chop pic
(i say that because i always make a new bg into the chop pic instead of placing the car into a new pic/bg)
try to start this way > next chop you do you keep the original surface the car sits on ( the ground like tarmac or grass) and keep the original shadows)
the change the backdrop for something new or build a new backdrop from several pics ..
the you can try to overlay different tarmacs on the existing tarmac etc etc
this way you can keep an eye on lighting etc...