This looks great.
OR you could have had a piece as long as the sofa and not as high, or you could have had 2 pieces with 1/2 the width of each piece as your negative space in between.
There is no one answer to this one.
You did just fine.
Regards
Karen & Joseph
for Decorative Philosophy

I agree with Decorative Philosophy: wider and shorter would look better. So that a head of a seating person doesn't block the picture and doesn't bump on it by chance

If you want to try something a little more unique, you could also try getting one of those pieces of artwork that extends between two frames, like two separate canvases. I agree with both Decorative Philosophy and Triquita as far as the size only that you might get a fresher look with two pieces over one sofa instead of one piece over one sofa. :)