I'm being called a cheater (highschool)

So last week I had a 3 hour long assessment that was to be completed in those 3 hours. I did complete it and I thought I deserved a high grade and was proud to hand it in. (For context I am in highschool.) My teacher hands the marked assessment back to me with feedback, and I see he graded me with a C. I am devastated as I was expecting an A. I then emailed him asking him to reconsider my grade. That evening I'm looking through my assessment to see where I went wrong, and I decide to change some things around. I added people's names to make it more personal instead of more general, for example: The customer was changed to David. I already included the people's names from the case study for each thing we had to review for the assessment, I was just adding more names to make it more personal, as well as including the corresponding pronouns and one more sentence. I get an email the next morning by my teacher saying he looked through my work and graded me with an A. I am so happy until I come home that afternoon and find out my mom got an email from him. He looked in the document history and saw the changes I made and is accusing me of cheating and academic misconduct and he wants to meet with me and the head of the subject department. I feel so scared and I feel like the whole thing got blown way out of proportion. What should I do? Was I in the wrong here?

I can think of a couple things. You asked if he would reconsider. You didn't say he agreed to it. Maybe he saw your second effort, and forgot about your request? Then he sees it had been re-worked, and thought someone was cheating.