Check the CINEMA 4D Renderer’s options. This is accessible either by clicking on the CINEMA 4D renderer selector in the lower right corner of the viewer panel, and then choosing “Renderer options…”, or by opening your comp settings, navigating to the 3D Renderer panel, and clicking the Options button.
Inside the C4D renderer options screen, there’s a quality slider. It looks like yours might be turned all the way down. I think the default setting is 25, but you can increase it for better fidelity renders at the cost of longer render times.