Great! I’m glad it went well!
I’m sure you are worrying and obsessing over nothing! I think it is very common to be nervous and “ramble on” and interviewers know that. You’ll be a great addition to any boarding school community.
I totally agree with Oak2maple interview is your chance to flesh out everything that they already have on paper. Make them understand you as a person, they already know everything you have done, tell them one thing you are really excited about what do they miss about you as a person from reading your application? I think you are smart to be reacting to their responses to you and adapting your interview approach as you go on, good for you!
Im kind of guessing here but you seem like a naturally intense person. That should be celebrated as who you are. No need to be laid back if thats not your spirit. These aren’t faults. It’s your sense of passion.