How to handle the fact that the advisor is disappointed?
This is part of the process. You will continue to make mistakes. It's likely that all your supervisors made similar mistakes when they were first learning and they likely will continue to make mistakes. Starting over from the beginning isn't ideal in terms of completing research or publishing papers, but it's often necessary, especially if you wish to learn from your mistakes instead of continuing to make the same errors.

I think I spent the entire duration of my master's studies making mistakes. Some of these were errors in estimating how much time an approach would take. Others were misjudgments of expected results. Most of my mistakes, however, were about what people expected from my research. I thought I needed to single-handedly provide enough solid results for a Nature paper. I was clearly incorrect.

I would encourage you, then, to discuss with your advisor what their expectations of your research are. You both should expect to make mistakes along the way.