If you contact the admissions tutor letting them know that you might not have performed as well as you should have done and that you're really set on Lancaster then they may look on your slightly more favourably than if you had said nothing. Otherwise how are they to distinguish between weak candidates and people who - for whatever reason - didn't perform as well as they could but are capable of more?
Did you attend an interview as part of the application process? If yes then they may well use your performance in that to help them decide whether or not to give you an offer if you don't quite get the results they want. I certainly know people getting into Lancaster with BBC for an AAB/ABB course but that was a number of years ago and in a different department.