It’s off because it reflects nothing worth seeing twice and a bigger one will just reflect more of things not worth seeing twice . Add another piece of art and get rid of the fake greenery and get some lighting that actually lights the space instead of the ceiling.

How about a nice mounted sailboat model to complement the artwork?

Another vote for a piece of art or two.

I put little mock up together. A mirror in that spot does not reflect anything nice and it is hung too high. I picked a piece of art for you and placed it at proper level. Art should be hung at eye level to middle of art. Most hang too high. I put an arc lamp over desk and a tripod style floor lamp. I removed other clutter. 🙃

I think what's "off" here is the lopsidedness created by the corner armoire and sofa. Any chance it would fit in the corner where you've angled the sofa? I would try it in that corner, and if it isn't specifically designed as a corner piece, I would center it on the mirror wall. Move the boats down to hang 5" above the sofa centered on that wall. Arrange the desk so your back is to the window, and place the two torchiere lamps flanking the window. I think centering the rug in the room would help a lot. Your room is "leaning left" due to the furniture arrangement, and the rug (although placed to the right) doesn't have the visual heft to serve as a counter balance. The mirror is not the issue, but I don't think it is required for this space.

I vote for art on that wall.

Thank you for your feedback everyone. I appreciate the mockup too!!!