The car is sitting at a strange angle in relation to the backdrop, no? Plus the image seems to be skewed for some reason.

Mia_mats aren't that bad are they lol. Maybe check some of your samples on them, like blurring reflections/refractions, you could just scroll on down to the interpolate section and do the bulk of the blurring there, much quicker than juicing up the sampling on the reflection/refraction gloss.