This anxiety is very common. In the best, most blameless organizational cultures, team members are allowed to say "I didn't get much done yesterday" on an occasional basis and are forgiven for it - but I realize that reality isn't often like that. In reality, sometimes you have to just BS things, as others have suggested, by holding some work back from your big flow-state pushes, or by dithering around with words lik…
Note that according to Scrum-in-theory the managers shouldn't even be at the daily standup. The entire purpose is coordination between the developers. You say "I am working on X" so that people who know or do something relevant to X are reminded to tell you about it (after the standup). Also, once in a while two people accidentally start working on the same thing (maybe the first one forgets to assign the ticket to themselves), and at the standup this becomes obvious.
However, Scrum-in-practice is usually something quite different.