I’m not entirely sure whether or not an undo button will ever be a reality, but in the interim we have previously added a Remove Ghost feature. Quickest way to currently do this would be to click the Ghost module on your Dashboard > (since it’s automatically sorted by level) click the items in question you wish to delete > go to its example sentence > hit hamburger menu > delete it.
might see about just adding a small delete button to the Dashboard’s Ghost Module to reduce steps (edit: yes, we will be adding something exactly like this asap! ty for the inspiration), but either way, yeah there’s one alternative if you happen to create ghosts you didn’t mean to.