If your steering servo is trying to move further than the steering can physically go (if its buzzing at full-lock, the servo is usually travelling too far), this is very bad for your servo. This will burn it up fast. End-point adjustment is a crucial setting to prevent such a problem. If your radio doesn't have this feature, then... not good... but if you don't know how to set it up properly on your transmitter, than its time to dig up that manual. This is what you should look at first, but if your steering is physically being limited because of some obstruction in the servo horns path of movement or the steering linkage is hitting something, than you'll have to figure out what is out of place and creating this problem.
These are the more common reasons why you have more steering in one direction than in the other, but there could be other problems, such as a faulty servo among other possibilities.
