There are two kinds of expectations you might have for your viva, facts and feelings. In the swirl of thoughts about the end of the PhD, and anticipation for what might happen, it can be difficult to determine whether an expectation is one or the other.
Is it a fact that vivas are long, or is that a feeling?
Are you certain your examiners will be looking for problems or do you just believe it?
Reflect on whatever expectations you have. What do you think you know about the viva?
Which are facts? What do they then mean for your viva?
Which are feelings? What do they tell you about what you might need to do?
What can you do to fine-tune your expectations, to know more facts and to have better feelings for the viva?