It sounds to me like you probably need to loosen everything, and then re-tighten when all is realigned, but as a first step loosen the steering stem nut (big one under bar, v. tight) to free off the top clamp a bit, and if your lucky the top and bottom clamps may just spring back into alignment, but if you have already tried the old holding the front wheel between your knees and yanking on the bars without success chances are you will have to do the whole process.