The largest feature of the room is the window + ceiling peak - use that as the basis, not the fireplace.

Are you settled on a chandelier for certain? I have a similar room (though a bit larger at 35x26) with 4 hanging light fixtures, one centered in each quadrant. The ceiling fan is hung from the ceiling peak, centered with the room.

Are you sure you don't need a ceiling fan in this room? If this room isn't open to the second floor I guess you would be OK without one, but I know I need one in my two story living room. Can you post some more pictures from different angles so we can see the whole room?

My chandelier is centered in the room, but not on my TV and seating area. On paper it looked like seating would be centered, but once I added all the furniture it made more sense to have it off center. Doesn't bother me and no one has told me I should have it moved! Also symmetry and "center" are only appreciated from one particular spot, so most people don't notice these things when they are guests in a space and moving about and socializing.

I'd hang a 42" fixture where your receptacle is.