There are some bugs in Dorico which cause the screen display to get out of step with the contents of the score. This looks like one of them. You probably didn’t do anything wrong.
Hopefully, the bugs will get fixed in future releases, though some of them don’t seem to be 100% reproducible, which makes finding them more difficult.
If you get a bug like this that is reproducible, posting the Dorico project on the forum (not just a screen shot) and explaining how to reproduce it might help the development team, if it’s something they haven’t seen before.