The direction provided by the google API probably wont be able to return your marathon route.
The directions returned are for driving, so will try to find the quickest way to get from point A to B. most marathons dont plan their routs on the quickest way, but the safest way for the runners.
One thing that you could try is to change the travel mode the directions are calculated with from diving mode to walking mode.
To do this, you will need to edit the map JS code that is created.
find the following line:
directions.load('from: ' + fromAddress.full + ' to: ' + address_0.full);
and change it to:
directions.load('from: ' + fromAddress.full + ' to: ' + address_0.full, {travelMode:G_TRAVEL_MODE_WALKING});
this still may not get your exact marathon route.