Don't think of it as public speaking, think of it as a performance. You wouldn't go try to perform a play without scripting it and memorizing your script first

Don't think of it as public speaking, think of it as a performance. You wouldn't go try to perform a play without scripting it and memorizing your script first, nor should you do that with your presentation. Once you do that you can ad-lib and it will seem natural. Even the off-the-cuff jokes aren't really off-the-cuff. And go twice as slow as you think you should, and pause a lot. When people get nervous they talk faster and don't realize it. If you're nervous your perception of time will change and small pauses seem like an eternity. Slow down and force yourself to break for five seconds between "paragraphs" and you'll be way ahead of most people.