Be glad they didn't try to have the cops come and arrest you. On the up side, you did not have any on you, so lacking physical evidence, you will not end up with a formal criminal record, even though it could hurt your college applications. Is this a public or private school? Did your 'friends' make statements tagging you as their dealer? Kinda sounds it to me... Nice friends.
If you are going to fight it, you will need to get an attorney to help. This is a matter for professional advice.