i really dont see the issue? I would put the furniture in, or tape it out, you could always balance it with art on the left. once curtains are up things will change.

Even if you knock down part of the wall, you won't be able to center the room furniture with the window arrangement. So I'd at least get my furniture in there first to see if that's a major factor.

It looks like the curtains were hung to pretend the window on the left was a matching double. That's a reasonable option and convenient since the rod is already hung.

From the inside you could do the same size rod and curtains on both windows (the double and single) to create the illusion of symmetry. It will trick the eye into thinking there is another window there where the curtain is covering. Then I would add a nice accent table or small chair in between the windows.