Here's what you need to do. With the front end supported on jackstands or the tires sitting on a conveniently placed oil spill, turn the steering wheel all the way left. Then turn all the way right. Now turn the wheel left HALF as many times as it took to go from full left to full right. This will put the steering system in the straight ahead position. At this position the steering wheel should be sitting straight. If it's not, the wheel may have been improperly installed. If the steering wheel is straight, observe the inclination of the wheels. If they are pointing one way or another then the toe angle is out of tolerance on one or both wheels. If this does not yeild a definite answer, then have your mechanic check the steering system.