Can a vice-principle legaly go through my cell phone with out my permission,?

I am 14 year old boy and just moved to Chapel Hill ,North Carolina from Austin, Texas and i attend East Chapel Hill High School which is a public school. Today at school i was called into the office for suspicion of marijuana, some one told the office that i had it on me and i showed it to them, so i walk into the office normally because i know i didn't have anything on me and had done nothing wrong. When i get into the vice principles office she does the regular routine as they would in Austin, Shoes off ,Empty pockets, Get patted down type of deal, which i was fine with and i happily handed over my pack pack for them to search. The police officer and vice principle found absolutely "Nothing" on me. At this time i think i'm okay to leave which is when she(the vice principle) picks up my iPhone and tries to get in it and asks for the password. This is something that never would have been even thought off back in Texas so i wasn't expecting this at all and i know its not good but i had *ALOT* of pictures, videos , and messages of me smoking marijuana with my friends. So i ask the police officer if shes allowed to go through my phone legally without my permission and i don't remember exactly what he said because he used allot of fancy words in ways that i think he knew i wouldn't be able to understand, but basically he said 'yes she can because they had suspicion' .But i was not under arrest nor did they have a search warrant or any type of proof or evidence that i had done anything wrong. So i tried to get as much information about it as possible from the police officer so i could better understand why she had any right to do this but in the end he kept saying yes she had the right , so i unlocked it and she went through EVERYTHING my Facebook twitter texts calls pictures notes and so on. She made comments about the pictures and texts but nothing in them linked to me having drugs on school property, so i was good to go since they didn't find anything but i just can't get over the fact that she was allowed to go through my phone right in front of me with or without my permission & i'm positive that she will try to pull me back into her office again for the same routine that she did today, and i was just wondering if she really did have such a ridiculous right to go through my phone and if there's any rights i have for next time that i can use to prevent her from going through my phone again, please give your thoughts & ideas on the subject