If you mention your nervousness or apologize for any problems you think you have with your speech, you may be calling the audience's attention to something they hadn't noticed. Focus your attention away from your own anxieties, and outwardly toward your message and your audience. Your nervousness will dissipate. Turn nervousness into positive energy. Harness your nervous energy and transform it into vitality and enthusiasm.
Experience builds confidence, which is the key to effective speaking.
A Toastmasters club can provide the experience you need.