Kaitlin Nootbaar said "hell" while speaking in May during gradation at Prague High School, about 60 miles east of Oklahoma City.
School officials had approved a written copy of her speech that used the word "heck." The principal says Nootbaar will get her diploma when she writes a letter of apology.
"I'm not sorry, so writing an apology letter that's just going to be a lie, which if they're saying that my cursing was sinning, that would be another sin, so don't want to have two sins on my hands," said Nootbaar.
The school superintendent refused to comment on the situation, calling it a confidential matter.
Nootbaar will attend college on an academic scholarship.