It’s very mature of you to ask this question on this site. I agree some responses are harsh but I think well intended.
In the US, a bad grade on one month of exams during the year would not pull down your overall average that much. My D has received 70s on an individual exams and still managed a 90 or above in every class regardless of a bad grade. The Transcript should only have the end of year average grade, not every grade.
You are a nationally ranked swimmer. The AO will see the time and dedication it takes to achieve that goal and the pressure it puts on your academics. Put down the number of hours a week you swim on your application. The AO looks at the whole application holistically, not just one month of exams. Good luck in your process.