I think i would use the beams to make it look more centered? run one from the center to the fireplace and then another to the same wall, look like it was meant. Hope we are both understanding here.

sometimes it just pays to ignore these things. can you add something to make it look centered? going nite nite, talk tomorrow if not solved.

We have a similar situation in our family room except our ceiling is flat with large beams in a tic tac to pattern. The 10 foot high stone wall at one end of the room, has a fireplace opening that was positioned approximately 1 foot left of center (framing requirements made this necessary). To camoflough the off center, we hung a large mantel that was the same dimension as the beams (10" x10") above the fireplace extending it about 3 feet either side of the opening When you look at the wall, the mantel tricks the eyes into thinking all is centered. The only time it's really noticeable is when we hang our Christmas wreath above the mantel for the holidays, but not really because there are so many other decorations in the room anyway. Hope that helps.