The light source shouldn't be off-center for any technical reason, it just might make it more interesting to look at. Your choice if you want to change it, but I'd stick with the light source you've got since you've already done so much detailing. The one thing that really needs asymmetry are the spots. If you look at the reference, they aren't supposed to be symmetrical, so mirroring them looks looks kind of lazy and less realistic.
Really great work so far, anyway!