Can someone help me figure out how to determine if the refund I received was correct?

Background: I flew last Saturday on a paid business/first ticket from YYZ-DFW-SFO. While at YYZ waiting to depart, I received an alert that the YYZ-DFW flight was delayed enough to make me miss my connection. I called and rebooked, though the only flight with open seats when I called was one that left me with a 5-hour layover.

Just before departing YYZ, the gate agent announced that the DFW-SFO flight I was originally on was now also delayed, so passengers would be able to make that original flight. I requested to be placed back on that flight, but the GA told me it was now full. I checked at the lounge in DFW on arrival and a seat had opened up, but only in economy. I took it.

Today, almost a week later I received a refund from AA for $104.50. How would I calculate if that's the correct difference in fare for the DFW-SFO leg of my flight (first vs economy)? I did fly business from YYZ-DFW. Economy in DFW-SFO.