Takehome Exam Plagarism Help
As an instructor, I usually appreciate when my students let me know about a potential problem in their work before I even have a chance to discover it myself. It signals to me that they're 1) concerned about their work, and 2) aware of their own work -- which, sadly, not all students are.

I can't imagine it would hurt to send that kind of email, unless your instructor feels a certain kinship with the Grinch.