Sounds like a self fulfilling prophecy to me. You don’t ‘know’ you will but you assume you will. If you think you will then you’ll be extra anxious that you will, and you will (probably). Instead think about talking too fast and put that anxiety into good use and slow your speech rate, use smooth transitions and get the brain working and concentrating on that stuff so it doesn’t have to time to catastrophise about a few words and you may reduce the likelihood of it happening (possibly). Even if you do, doesn’t mean anything terrible is going to happen! The worst outcome here is you bail and avoid it altogether.