Extending the length of a duplicated project - export error

Hi team, I duplicated a 25min project that I wished to extend to 30min. As I was extending it with extra media, the new media would be outside the 25min range and would appear in an area covered with diagonal black stripes. Once I reached 30 min, I wanted to 'share' my project and export it to Quicktime, however it still comes up with 25min in the properties. How do I extend the length of the project to include the entire 30 min within the clear timeline? I tried exporting it as it is, but an error message came up (see attached screen shot). I am really worried as I am screening my film tomorrow and can't seem to export it... any help would be really appreciated, Thanks for your help!

It sounds as if you haven't actually edited inside a project but inside an individual clip. Copy and paste the content into a project Cmd-N.