Okay, hon, take a deep breath, okay? Stress is one of the many things that can affect your menstrual cycle, and it sounds like you're majorly stressed right now.
Okay, now for your questions. First off, unless the guy in question ejaculated on the towel or used it to clean up after sexual activity within an hour or so of when you used it to dry yourself, chances are very, very slim that there'd be any viable sperm on the towel. Sperm needs a very particular sort of environment in order to survive for very long, and towels in a bathroom simply aren't that sort of environment.
And also, menstrual cycles don't always last exactly the same number of days, particularly when you're young. You say your period was due on December 3rd, but that's only four days ago. And like I said earlier, stress frequently messes up menstrual cycles.
If you're really concerned that you might be pregnant, the easiest way to find out is to buy a home pregnancy test and take it. They're simple, cheap, easy, and usually quite accurate, particularly since the incident you're worried about happened back in October.
But hon, I really don't think you have much of anything to worry about. It sounds to me like your menstrual cycle is simply fluctuating a bit, as is perfectly normal for young women.
"The only unnatural sexual act is that which you cannot perform." - Alfred Kinsey
[This message has been edited by kythryne (edited 12-07-2001).]