If you've ever been an athlete you know how much energy you receive from the spectators. The same is true of public speaking, though it doesn't seem like it at first. Even after a few times out you will discover that the audience makes your mind sharper and your talk better. That's why rehearsing your talk to a friend by way of practice often backfires -- that one person can't replicate the energy of a full audience. That's why I do a mental rehearsal rather than speaking it out loud.
Let your enthusiasm be contagious, but don't adopt a gee-whiz "Isn't this amazing" TED talk persona.
Don't aim for JFK gravitas unless you're speaking at a funeral or maybe your daughter's wedding. Watch Pete Buttigieg speak in the Democratic debates. He is overall an excellent speaker and a master of tone.
Be sure to totally master your intro; that will give you confidence and get your audience on board. Remember, they WANT you to succeed because it is almost as painful to listen to a floundering speaker as it is to be a floundering speaker.
Somewhat surprisingly, I discovered in that course that it's far easier to talk about something I know and care very little about. Not sure what to make of that.