Am I in the wrong?

(warning: this is a long rant and situation)
This is about my principal and I. Some context: our school is an independent school and we pay very high fees to attend this private institution. (We are not in the UK btw)
Our school hosts an Easter revision course every year and other outside students must pay hundreds to attend. Us full-time students can gain access for free. I booked mine the second we received the register link (we're only allowed to book our preferred classes after the outsiders). I booked my courses in the order of Chem 1, Chem 2, English and then Maths after lunch.
However, when I received my schedule, Chem 2 and Maths were switched. This was a problem for me as firstly, Chem 1 and Chem 2 in the morning are on in the same room so I didn't have to run across the campus. (The school rented a University campus for the courses)
Secondly, my friends had all booked the same classes of Chem 1 and Chem 2. However, they booked if AFTER I did. They were not switched though.
Thirdly, I did not want to take Chem 2 in the evening because it wasn't the same teacher teaching it. I know FOR A FACT that the morning teacher is better.
I went to get my schedule changed but I was unlucky enough to encounter my principal. He told me that it makes no difference and that the Chem 2 class in the morning was full, hence why my timetable was switched around. However, this does make a big difference to me. I KNOW that I learn better with the morning teacher. I know this teacher's style. However, I do not like the evening teacher's style at all and cannot comprehend her. He gave out to me and told me to just deal with it.
Mind you, other people were going up to the secretary to get their schedules changed. I just happened to meet the principal at the door of the office. So I never got a chance to ask the secretary whether it would REALLY be possible for me to switch back.
Mind you again, when I went back to collect my stuff from Chem 1 (in the same room as Chem 2 will be taking place), the room wasn't full at all. Surely they could squeeze me in. The morning teacher even said that she doesn't mind if I stay. She said she won't bat an eye.
So after that whole conundrum, I was ultimately late to my second class on my incorrect timetable. I didn't want to walk in after the class had started (these are lecture halls sooo) so I asked the assistant secretary whether I could go in or not. She said she'd walk me in but I had second thoughts so I told her that it's ok. I told her my situation and she said that I can go get my timetable switched-- but I told her that the principal wouldn't allow me to. She then said that if she's the one going around checking whether everyone is in the right classes, that she'd pretend that I'm in the right class. However, I was scared because my principal is the other person who goes around checking...
Afterwards I told her that it'll be fine, and I'll just go to our school building and practise the piano instead of attending the revision courses today.
Context here: My in-school music teacher told us that our school and the piano would be open and available to us this Tues-Sat. Our state exams for the music practicals are on Mon and Tues. The piano only arrived at our school last week and we took turns getting used to it. However, it's not a very good piano so we're still not fully used to it. So I decided to go and practise. However, there are GCSE equivalent revision courses ongoing in our school. (A-level courses in the Uni, GCSE courses in our school).
So when I arrived there, guess who I met again. Yep, my principal. I was just so unlucky that he also decided to leave the uni and head to the school to check on everything. When I got there, he gave out to me and told me sternly that I would not be permitted to practise. The only time that I could utilise the piano is during lunchtime. This poses a problem though. There are like 8 of us who need to play the piano. One hour per day will not be enough for all of us. Also, most of us are at the Uni so unless we skip a day (like I did today), we would not make it to school in time for the lunch time.
Am I in the wrong for trying to prioritize my own studies? Should principals not try and do the utmost for their students, especially when the exam is so soon? All the teachers understood me and were willing to help me but he's the only thing standing in the way. Mind you, I was not looking to talk to him at all. I was just so unlucky to have been stopped by him and to have bumped into him so many times today.
I normally don't like causing conflicts, especially with people older than me, but I just feel so wronged and angry right now. Yes, i'm probably acting entitled, but we did pay thousands for this independent school that promised us the best. They were all empty promises after all.
My principal said to me: "I don't know what is the problem between me and you today (insert name)." And other stuff. However, I don't understand why he was mad at me. I'm just trying to fight for my future? I didn't pay thousands just to get a half-assed education. I need a good mark in my music practical next Monday. I need a good mark and a good teacher for chemistry.

You are in the wrong.
Imagine if displayed these types of behaviour and attitude to an employer?