By any chance, you gonna be presenting with your masks on? If so, you could bite on some hard object maybe like a small stone onto your last set of teeth and press it hard. It'll prevent you from closing mouth and sometimes give you the breath you need to let *that word* out. Can't say if it's super useful but it kind of worked for me . Also, don't think too much about it, your life >> that small (yes, not big) presentation.