Like anything we do in life, skills become stronger the more they are practiced. Don't expect to play the piano well after one week of study.
So, your reality is that you have a presentation in 2 days, maybe it's 1 day now. Yes, adrenaline and cortisol make our bodies go faster, our thoughts race, our anxiety increased. If you can do anything to slow that down, you will likely do better. Using slow talk is a great strategy to use in any situation which has us naturally starting to speed up more than we would like. So, there is no reason you should not use slow talk, and every reason you should. Even if you did not have social anxiety, when one speaks a bit more slowly, the talk with likely sound better and clearer to the audience.
Still, since you have just started therapy, perhaps you have not practiced slow talk as much as you will have, say 20 weeks from now. Naturally, you might not be able to slow down as much as you'd like at this point. That is natural. Whatever happens with your presentation, keep that in mind. You are only human, and you are doing the best you can. You can't change habits overnight. So, don't get mad at yourself. Don't let whatever happens during the presentation get you off track with the therapy. Don't set up some sort of unattainable performance level that you measure yourself unfairly by now.
Good luck with the presentation. We'll be here when you get back!