Hi Gina!
I believe that as long as GoToWebinar is designated as the webinar program's Event Partner, you shouldn't have to create a separate Marketo form to change their Program Status. It's been about a year since I last used GTW and Marketo together, and I think some things have changed, so I may be mistaken.
However, if I'm correct, then Marketo should automatically be able to pull in and update the status from GTW.
If it's only saying that people attended (and not attended on-demand), you may want to set up an operational campaign, though, that says something like:
If Program Status was changed to Attended after [the date we did the webinar live], then chance the Program Status to Attended On-Demand.
Not sure if this helps or not, but I hope it does!