Are you sure you mean 21st percentile? Percentiles measure the percentage of people you’re ranked higher than. In this case, you’re saying you have a better GPA than only 21% of the people in your class, which is in the lowest quarter. Did you really mean the 79th percentile? (100-21=79?)
Also, good luck with Swarthmore! I got in EDI, and I’m excited to see who gets accepted EDII.