Square shadows in rendering I'm making a cushion and when I render it, there are square shadows. Is this because I didn't subdivide surface enough? Or did I touch something wrong? In Edit mode, it looks already to have a lot of faces. Is there way to smooth the shadow?

I'm not using lamp object but world with Pro lighting Skies add-on.
I turned off the Pro Lighting add-on. I suppose because the uni machine I'm using doesn't allow to use or something... though it looked installed. Thank you for the help!