There's no undo. Using -recall would simply have called up the last used options. If there was nothing in the todo list and you provided no url it would have done nothing significant. If there was something in todo or you supplied a url those sites/pages would have been walked with the options you last used.
If something was walked you could delete the new records by comparing to the Visited field. Something like:
gw -st "delete from html where Visited>'2002-03-20 17:07:00'"
Deleting associated refs at the same time would involve a little more work and probably a small vortex script.