How should I write my "low grade" essay?

In May, I had my A-level exams, so my school gave me permission to skip economics class. I accepted the offer, but it turns out my final grade for economics was 88, whereas in the previous semester it was 94. My teacher told me I could improve my score by completing an improvement task, which I did. However, the score didn't change because the academic team, responsible for entering grades into the report cards, wasn’t aware of the improvement task due to a miscommunication. I'm afraid it'll affect me greatly because I'm going to major in Finance or Economics. Should I write the "low grade" essay? And how can I approach it in a way that doesn't make me seem like a "red flag" to the admissions officers?