You could try ...
It might be a learning curve for next time though ...
As a backdrop for a portrait I go for a texture - like a brick wall... Nothing - white, black, etc to draw attention
Or somthing that would make a good photo by its self - a vanishing point road, archway in a church ... That sort of thing
The fact remains here though that the framing and focus is spot on ... The flat lighting, expression and darkness of the eyes work well to create a look of slightly cheeky, yet very slightly menacing ...