I mean the ground reflect in the Image BG the light from the sky very intensive , the shadows under the car are much more darker there is not light from the sky not from the sun  , the position of your model is in a lucky spot where the part of the shadow excist already but the final render have a double shadows now.. so the parts of the shadows under the model should be darker and the rest need to match the other shadows of the image that have a ::blue tint:: and with shadow catcher feature it is not possible to do that correct.
You should render this out as a layer without the background image, remove the shadows from the places where they are already in the BG image and tint the rest of the shadows to match it and perfect image is finish..

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