How will a 'fail' in a course affect chances at graduate school admission?
Short answer, since I've already addressed a similar case in the answer mentioned above: this should hurt you very little so long as you can maintain your current record throughout your undergraduate program of study. When I consider graduate applications, I am not interested in how a person performed at age 17 or 18; I am interested in how he or she will perform in my program. Four years of high marks and outstanding additional activities are a good indicator. One bad grade from high school is irrelevant. 

If the transcript is sufficiently vague that someone could possibly be confused about this, have one of your letter writers mention the situation in the letter. But my personal feeling is that even this is unnecessary.