Sharp stabbing pains in the chest area of children and teens, as well as adults is generally related to muscle of cartiledge issues. True heart related chest pain is not stabbing in nature at all. I really don't think you have too much to worry about. At your age, things that would cause heart related chest pain would be extrememly rare and you would have already been aware of the issues that would cause it just in your daily living.
It could be a sign of something. Make a doctor's appointment to get checked out.