Nervous isn’t a prediction. Your stomach doesn’t know how the presentation will go.

Nerves are your body getting ready, not your body knowing something. The same racing feeling turns up before things that go badly and before things that go beautifully, which means it carries no information about how this will end. Treating it as a forecast turns your own preparation into evidence against you.

Rename it as it arrives. This is my body switching on, and it will settle a minute after I begin. Then do the first thirty seconds you rehearsed, since that is the part nerves make hardest, and the rest tends to follow.