When I drag out a circle, or use the node to curve the corners of a rectangle, the line isn't smooth. It looks like it's slightly jagged. I've searched online and in this forum for a solution, and I'm sure it's simple, but can someone help me with this?

I'm trying to create a drawing which features the rounded edge of a playing card, with no luck. It simply doesn't look good.

Any ideas how to fix this? TIA