Concave fillet cannot be exported to .3ds or .dae

I have a concave fillet in the edge of a seat. I am trying to export it to Cinema4D for rendering. The problem is that the mesh which will be imported to Cinema4D is not exact in the middle section of the fillet. Instead of a clean radius the mesh has a shortcut wich results in a straight part in the middle of the fillet. How can I repair the mesh or make it smoother to follow the radius more exactly?

I found out I can remesh with a higher resolution (2000), then the problem disappears.