What can I do if I can't get a project done by its deadline?

I'm a software developer for a small company and I've been tasked with a new project a month ago. It's a pretty complex project and there are many moving parts which I don't understand and am having to learn as I go. My boss has set a deadline for the project (or else). If I can't deliver this project on time, what's the worst he can do to me? Terminate me? Take me to court? Etc.? I've never been put in a "or else" position before with deadlines and this has me very nervous. Any advice on how to handle this, would be appreciated.