To mitigate the risk of the team not feeling confident about the product increment, the project manager should schedule an additional interim demo with the product owner. This will give the team an opportunity to validate their work with the product owner and receive feedback early in the sprint. This feedback can then be incorporated into the work before the end of the sprint, which can improve the quality of the product increment and increase the team's confidence in it.
Additionally, it's important for the project manager to communicate the need for an additional demo with the stakeholders and to make sure that the team has enough time to incorporate the feedback into their work.