On another thread someone said "Berlin was short because someone's friends GPS was short".
No! The problem is guys like you become race directors and start using GPS to measure the course instead of the more accurate wheel. So most courses are too long now!
I ran one 10km course through thick trees with no possibility of a GPS signal that probably measured 6.7 miles. But it was exactly 6.2 on the Garmin! Experienced runners had raced in previous years were much slower and they knew it was long. The hobby joggers were like "finally a course that isn't short".
GPS might be more accurate if you race across a farmer's field.
With trees and building, GPS is misleading.
So throw away that GPS and measure with a flipping wheel.