A school principal is read as authority that judges and sets the rules. Dream books link the figure to being called to account, or to your own sense of discipline.
Does the traditional reading fit your dream, or did it mean something else to you?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.