I'd crop a photo of your art lying flat on the table so that the artwork fills the frame and use that as your first photo. Be sure, also, that you're using natural light for your photos because it's really critical for showing the colors in your art. Rather than standing at the table and shooting downward, I'd sit down and shoot more straight on. You might try adding a few simple props to your card photos, say a pretty pen, a nice desk blotter, a few stamps.