Actually this could be normal. The live axle on the car isn't necessarily dead center to the body. Mine's not, there's a bit more gap on my right side. For you, what's a little bit? Are we talking an inch or less? If so, I'd say it's normal. Also, when installing my panhard bar, the instructions from MM specifically say to measure the distance between the tire and bottom of the fender arch (horizontally) for this reason, and go on to say that it wouldn't be surprising if the measurements from each side weren't identical. Without knowing your difference, initially, I'd say don't sweat it.