In a cloudy day where there is not direct sunlight, you should not have strong harsh shadow and strong highlight. shadow should be more diffused as the light source are bounced from the environment.
Check the brightest white point of your image and match your render's brightest white point to that.
and the car must be bigger.....check the perpective....the car is "far" from the rest...so it have to be bigger than all other cars on you background....
the markings of the parking area show u how big your car must be....