Also remember to save your images with File>Save image>save color managed images.....your render is too dark because of color management features and when using car paint material, they are supposed to only go on the actual painted areas, not the bumper or any plastic looking part of the car, that includes the rubber parts as well , use standard Mia X material for those other areas, there are presets built there for you.....and try to render the car with an IBL not with the physical sun and sky.
Cars need something to reflect, like surrounding architecture or at least clouds in the sky, the physical sun will give you uninteresting render results.
Lots to learn....Happy renderings.
