When I have been in a situation when I needed to tell my PsycT something difficult and wanted to explain it properly but yet be spontaneous, I have written bullet points and then gone through them at home speaking it out loud. This way, I was able to get continuity of what I wanted to say and how I wanted to say it. I took the bullet points with me to refer to and followed them but spoke around it, if you see what I mean. I found that when I was with her even though I followed my bullet point notes the conversation became spontaneous because she commented or said something and it was all very natural. I told her before I started that it wasn't easy to speak about this particular subject and that I had made bullet points. She thought that was a good thing as I had thought about it and prepared.
One thing she did say which stuck with me in a good way is that me, the patient/client, does not have to be appropriate. She said it was her job to be appropriate. Obviously there are limits to me being inappropriate but I wouldn't be that extreme anyway as I have respect for her as you do with your T.
I have said sorry to her but not in a way that was humiliating for me because T's expect ups and downs, that is part of their role and if we are being perfectly open and honest with them then these ups and downs are going to happen. For instance, I thought she was going to react to something I wrote to her about in the same way as my abusive T had done. My left side of brain, the logical side was saying of course she won't but my emotional right side of brain couldn't see this reasoning and won. I told her all of this in the letter and apologised and said it was me and my bad abusive T experience and life insecurities and not her. I explained this again briefly when I saw her but I think it was water of a duck's back to her, she had probably heard much worse and the same probably goes for your T. They have heard it all time and time again and to them it is part of being a professional and they don't take it personally. We take it personally for them because we love and respect our Ts.
Hope this helps a bit.
Good luck tomorrow, I am sure it will all go really well for you, do let us know.
Caroola x