If it's crystal do you have all the jewels? If one is missing that can shift the center to one side. More likely is that one or more of the arms is out of position. The arms should be equidistant at the outside. Don't just push on the arm - it could break. It may take some disassembly to get things right so if you don't have the skills ask a lighting shop to make it right for you.

There are no jewels... there was no assembly on our part, it came all in one piece. The arms look like they are soldered on. Will try asking a lighting shop, but it might cost more to fix it than it cost us to buy it. :-(

As David noted small weights added to the outermost point may offset the imbalance. It's difficult to say what kind of weights will work the best. You may be able to hide either lead splitshot or florists putty around the socket if there is room.

Make sure there is some slack in the wiring feeding up the hanging chain.

It should NOT be pulled tight (more like barely snug).

There is some slack in the cord I think... I'll check when we go over there this weekend.

I know this an old question but I had a similar problem when installing a 9 light lamp and was unable to find an answer. After a couple of hours trying to figure it out, my wife returned home and noticed that the spacing between the arms were uneven. I adjusted the spacing and resolved the problem. She should never leave me by myself :)

How did you adjust spacing ?