You are unable to edit your project because of possible below reasons:
1. Published Project with at least 1 Backer: When a project is in draft mode, it is not finalized so all the details related to that project are editable. But, once a project is published and is backed by at least one backer then few fields are non editable like: Project Duration and Funding Amount.
If Project Owner still wants to edit the published project then he can contact to the site admin. Site admin can take proper action in such scenario and do the needful changes.