I can’t imagine what someone could say in the viva, without going to flippant extremes, that would be so wrong as to lead to a terrible outcome.
Wrong couldn’t be saying too little or too much; your examiners will help steer the conversation.
Wrong couldn’t simply be factual error – your examiners would rather check details than simply let an inaccuracy through.
Wrong couldn’t be the result of nerves: your examiners are human and would understand. They’d give you space to get past nerves.
Wrong couldn’t be simply saying “I don’t know” – that wouldn’t be wrong, that would just be not knowing something.
It would be wrong to be arrogant, it would be wrong to pick a fight, it would be wrong to assume that you know what’s what for everything connected to the viva!
But would you do that?
If you are worried, consider what you could do to lessen those worries. If you’re nervous, explore how to build your confidence.
And if you’re still worried about being wrong, remember that it’s far more likely that you would say the right thing than the wrong in your viva.