YaS's advice is right on. For future applicants only tell a school that they are your top choice if they really are. Then only tell one school that. You are likely correct that you received some offers because schools thought you would go there. At this point, though, it is what it is. Just politely email thanking them for their time and consideration and tell them you've chosen somewhere else. Don't worry about the impression you made at this point, there is nothing that you can do now.