Make an object reflect less light

I have created a studio setup to render an object in UE4. Part of this setup is a black canvas that is just supposed to cast a light shadow beneath the object. Otherwise it should be just barely visible. So the end result of the rendering is supposed to be just the object on a black (or dark grey) background and with a little bit darker spot under it. But as you can see in the pictures the canvas is lit up very much by my light on the left, so the background now is more light grey and way more visible than I want it.
Is there a way to set up a material or change something else to make the canvas much darker?