OK.....well, I agree that you will never get all of that said without either forgetting about half of it because you will be under pressure and trying so hard.....or else you will hit a trigger button with her and she will interupt your speech. It is long.....(and that is the way I am too, so I understand it)and because of its length...it may sound like a speech to her.
I know the reasons you gave for not hand-writing it and telling her instead, but if it is very important to you that you touch on all of these things....I don't see what would be wrong with you hand-writing it and putting it in an envelope (don't let her open the envelope)and placing it her hand. Don't put it in the mail or fax or email....it makes it more personal to hand write it and then you place it inside her hand. But, if it is not in an envelope, it will be to easy for her to start reading at that percise time...which you don't want. Another reason I suggest a hand-written letter is that she can go back and read it over and over again. If you talk, instead, she will forget exactly what or how you said it and it will get mixed up in her mind later (perhaps, but why take a chance). Since I don't know her, I am not certain about that part, of course. You have to use your own judgment about all of this.
As you place it in her hand, she will ask what it is.....and you just tell her that is your attempt to apologize (I know that may be a tough one for you, but it may catch her off guard long enough to finsh your statement.) and that you would like for her to read it in private. (Don't say anymore! That will be hard for you to do, but don't get into any discussion at this point. If she starts asking questions about the contents of the letter, don't answwer, just look sweet and smile.) If she should say something that you just have to answer, try to tell her it is in the letter for her to read.
Look sincere, but smile sweetly......don't act "too" upbeat....but don't act like a whipped dog, either.
I guess what I am saying....and others may disagree, but I think if there is ever a time for you to kind of "wear you heart of your sleeve" it is now. IMHO, She needs to see that your heart still holds feelings for her (just a little hint of it anyway). I'm not suggesting that you break down and cry, beg, and all that crap....don't do that for goodness sake! Sweet and sincere......keep it short....and then....leave.
It's a tall order for us "talkers"....lol. And...this is just my thoughts about it.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!