Theory 1: Your fitbit isn't calibrated to your steps.
Theory 2: Something went haywire with the phone GPS (Happens, a friend of mine finished a marathon and her GPS watch said she ran 27.5 miles when the marathon was certified as 26.2. Buildings and trees can interfere with the GPS signal)
Option 1: Use google maps/google earth/mapmyrun/etc to map out your route and get the distance that way.
Option 2: Split the difference between the 2 numbers and call it a day.
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