iMovie

I am trying to export a 27min video from iMovie and it says that I do not have enough storage space to export. So, I remove photos and music to provide ample space. Then I try to export and it fails and the portion of the video that was be processed for export goes into my iMovie cache and adds all that disc space back in. Is there a way to delet these partially exportable files from iMovie? When I open the app I cannot see them to delete them, just the original project. The used space in iMovie has now tripled and my phone is completely plugged. How do I delete these files without deleting the original project??