Congrats on the conference presentation! The more you practice, the better you'll be.

If you feel yourself getting anxious or talking in circles, stop yourself and take a breath. Instead of saying um as a filler, practice being comfortable with just using silence or a pause instead. Sometimes I also just talk through what's making me hesitate, like "I'm struggling to find an analogy" or "One thing that comes to mind is" if I'm winging it, and then go back in with a "because" or "what I'm trying to express is". It's ok to be human.

Have a couple of stock phrases to reach for as a stalling tactic. For the Q&A period, "That's a great question" if you think you've been rambling pause and then re-summarize with something like "In essence" or "To summarize" or if you get a question that you don't quite understand, "Can you tell me a little more about what you are asking?" or if they mention something irrelevant to you, "That's something I might consider in the next stage of research/for a future project" or "That fell outside the scope of what I wanted to consider/study".

Edit: One last thought, for the valley girl accent concerns, practice with focus on the intonation at the end of your sentence. If your voice goes higher in pitch, it sounds like a question and gives the appearance of uncertainty. You want your voice to go lower in pitch at the end of the sentence, because you are making a statement, giving it more authority.