The "I didn't mean to yell is a complete sentence, but the character is adding an extra thought at the end. Should it be a separate sentence? Separated by a semi-colon? Though I wonder about that because what is on the back side of the semi-colon isn't a complete sentence. Is it just a parenthetical remark like this?"Take it with you!" I didn't mean to yell; scared the hell out of Tim.
I didn't mean to yell, (scared the hell out of Tim).
I seem to have confused myself.
Thanks!