You become uncomfortable because you focus on how you think the audience will perceive you and whether you actually know more than they do. This makes you feel that the audience is there to judge you.
There are several things you can do to improve your comfort level when presenting.
1) Speak to your audience as if you were talking over a cup of coffee. Remain professional but relaxed.
2) Don’t try to impress. If what you say is relevant to the audience, they will want to listen to you.
3) Take a deep breath and slowly exhale before you begin speaking.
4) Take a moment before you speak to make eye contact with individuals in your audience. Look straight in to their eyes, don’t sweep your eyes over their heads. You will find it helps your comfort level to feel your audience’s warm eyes upon you.
5) Remember, your audience doesn’t expect perfection, but they do expect value. So make sure what you say is about them, not you.