Writing an apology letter

Hello, I am a student who went to school obliviously intoxicated from a perscription drug I took the night before I arrived, and I am trying to write a letter to the Principal of the school to apologize to him, tell him that I didn't know I was intoxicated (It's true), and to ask him to not extend my time in the transitional center.
I'm going to post the letter as I have it right here. I would appreciate it if you can please tell me what words should be replaced with what, if I get passively aggressive, if and where it looks like I'm trying to butter him up, if I seem to be too wordy, and how to correct these issues for a better, more acceptable, and correct letter. I want to make this apology as sincere as possible, please help!

Also, ignore the mumbo jumbo until you get to the bold letter.

Dear xxxxxx,
This is a letter from xxxxxx, I am a student who attends the Behavioral Intervention Center that you manage.

I am writing to address a recent incident I was involved in, and apologize for it.
I assume you have been informed of the situation that has occurred Friday Nov. 20, when I arrived on the premises allegedly intoxicated. I had not taken anything that morning before I arrived, however; the night before, I had taken two, .5mg Clonazepam. I was not aware that the effects would remain the length that they did. I thought that the effects have dissipated by that morning ,but albeit I was oblivious to them, they had not. I promise with highest regards to you that it certainly was not an intentional violation.
With this letter I am expressing my deepest regrets and apologies for arriving on campus under the influence, and I request with consummate respect for your authority to please take my behavior at BIC to date into consideration. Also please consider the fact that I have been in transitional school since the beginning of October. This has created some very stressful emotions for me that I have been working hard on controlling. During all of my time at both BTC in xxxxxxx, and BIC here in xxxxxxx, I have worked very hard to complete my time,leave the Center, and just get back to regular classes. I respect your authority and know there must be consequences. I am just asking that if there is any type of consequence that would not involve extending my time in BIC, that it be considered. I'll stay after and help clean the building, remain in level 0 for the rest of the sentence, or do extra school work if you like. I just want to get back to school. With any decision that you make in response to the incident, positive or not, I assure you this type of thing will never happen again.

Sincerely,
xxxxxxxxxxx