Webform CiviCRM 'Registration Status' for Event not Updating each subission
I'm not sure from your description how exactly your form is configured. For the update participant status you may need a second form and specific url to reach it which includes the user's contact id and the event id.

See the responses to this question for more (and clearer) details:
How do I get Retrospective feedback for an event using a Webform (participant Custom Data)?