You will need to use every opportunity to build the campaign and gather new supporters. Create a leaflet or online signup form so that you can keep adding to your lists. But you will also be more successful if you regularly review your events and activities to analyse in a detached way what has worked and what could have been done better to inform your approach next time.
Building in a ‘learning loop’ with participants giving constructive feedback on improvements can help create truly successful campaigns and avoid repeating the mistakes of the past.