I hope you can take comfort in knowing that even the most seemingly confident people can really struggle with public speaking. Your adrenaline gets high, anxiety starts and your body enters fight or flight mode, your voice shakes, hands tremble, eyes blur. It's a very physical feeling.
I've learned about something called the 'illusion of transparency' which a lot of people feel during public speaking. It's a phenomenon where you believe that the people you're speaking to can tell how anxious you're feeling, can read what you're thinking, which makes your anxiety much worse. In reality, it's an illusion, and 99% of the time, people really don't notice the anxiety you're feeling. Fumbling a line can occur naturally, even politicians do it, it's not necessarily an indicator to others that you're very anxious.
For me, learning about this phenomenon gave me reassurance that indeed it's an irrational thought to believe that people can read your feelings and thoughts, and it's amazing how truely you believe it in the moment. It's easy to feel like our anxiety and nerves are very obvious, and other people are judging us for it. I hope you find peace in knowing that it really isn't as obvious as you may think it is, and challenging that belief may help you to relax a bit more.
I think all in all, depending on the person, speaking and presenting to a crowd it naturally daunting. We care about our presentation, how we come across, what people think of us. The others have given some amazing advice about how to relax yourself, which I've found to be very helpful. I think it does come down to practice, focusing on the people you're speaking to, rather than yourself and what they think of you. It's helped me to realise that I do take interest in other people, and that should be the main thing I focus on, not myself. Sometimes it's easier to put yourself in the position of the listener in the beginning, and you may find it's easier to share about yourself afterwards.
That was a bit of a ramble, I hope I made some sense and maybe helped you in some way.
It's a skill ultimately that you want to improve at, and I have full faith that you'll get there. People care and value your perspective more than you may realise, and I hope you're reassured that your sharing with others is well received, and that your confidence will get better.