yep, you need to relax. i know it's easier said than done at times like this, but remember: stress can impact menstrual cycles and cause you to bleed late or skip a period entirely.
two words > emergency contraceptives. if you're not familiar with that term, they're certain birth control pills at a higher dosage, and are proven effective at stopping a pregnancy from beginning if taken between 72 and 120 hours after intercourse -- the closer to 72, the better they work.
to get them, call your local planned parenthood and explain your situation. the pills don't cost much, and in some cases, they'll give them to you for free. if you're not aware of a planned parenthood near you, check your phonebook or visit http://www.plannedparenthood.org
to find the nearest one. if you can't get to one, try your local health dept (phone book > govt offices). if that fails, contact your family doctor or school nurse. Better yet, head to http://ec.princeton.edu/providers/
and enter your zip code and they'll give you a list of EC providers in your area. BTW, You DO NOT need Parental Consent before receiving emergecny contraceptives.