You may need to make sure that your whole project is selected when you choose to share the project. If there is only one clip in the project selected, then iMovie may try sharing just that clip. You can see the length of the clip you are about to share in the popup window, below the preview window right next to the black clock face icon:
If the length of your whole project does not match the length listed in that window, then you know your whole project has not been selected to share. Take care, and thanks for visiting the Apple Support Communities.