Is it pulling or does it turn when you have the handle bar in the correct center location?
If it is turning, then you should be able to adjust the issue via the steering cable. I have one that needed adjustment but did not have enough threads remaining on it. I used a die (as in tap and die) to make more threads as there was plenty of rod left to do so. Put it back together, problem solved.
If it is dragging, then there is another issue. Such as a broken part in the rear or something to that fact.