There's no prescribed way to document Retrospective feedback, but there are some things to consider.
The most important thing to consider is that the team needs to be able to be open and honest. If you are using an electronic tool and requiring people to complete retrospective notes before a meeting, then it is likely that the authorship of those notes may be tied to individual people. The people involved may be more likely to not be completely open and honest if they know that others from outside the team can see what they are writing.
That said, it is important to be prepared for the retrospective to make sure the time is well used. Perhaps allowing the team to add notes to an electronic tool is a good way to do that. But it needs to be balanced with the free, open, and honest communication between team members. I would think that it is unreasonable to have a "finished" retrospective page before the meeting and not be editing it during the meeting.
From my perspective, the most recent team that I worked with used Confluence for retrospective notes. The retrospective page was posted early in the Sprint and the team could optionally add notes to talk about so they wouldn't forget things. However, at the retrospective itself, I (as the Scrum Master for the team) was making additional notes and edits so further discussion couldn't be tied to individual people. The only expectation was that the team come prepared to have the discussion, and it seemed to go over well with the team.
The team should be empowered to choose their way of working to the extent possible based on the constraints of the organization. Your Scrum Master should not be dictating the way your team works, but coaching you on effective techniques and enabling you to do the work that needs to happen.
Focus on the problem and try to come up with good solutions, as a team.