Read something out loud alone. Getting used to the sound of your own voice makes it easier to use when it matters.

Your voice sounds strange to you because you almost never hear it when nothing is at stake. Reading out loud in an empty room takes the audience away and leaves only the sound, and after a while the sound stops being a distraction. Then in class, or asking for a shift change, your own voice is not one more thing to manage.

Pick half a page of anything tonight and read it aloud with the door closed. Do that three or four times this week. Notice where you rush, and slow that part down on purpose.