Let the details earn the confidence that the presentation asked for.

Confidence is easy to assert and expensive to justify. A polished delivery buys attention for about ten minutes, after which people start looking for the numbers, the method, the awkward case you have not mentioned. If those hold up, the assurance turns out to have been well placed. If they do not, the confidence itself becomes the reason nobody trusts the next thing you present.

Before your next presentation, spend the preparation time on the weakest number rather than the slides. Know what you would say if someone asked how you got it. Sound as certain as your evidence allows and no more.