Start/finish is the start/finish of this track. And bounding box is about the aera caourse should use. You can use gmap-pedometer for drawing the course (use "straight lines" option), just paste link to your course here. Distance about 15-20k mesured automatically "(for runners)". I'll use OSM map, fourth zoom level from the top.
Ok, a bit later. Course is here. Measured distance is a bit longer than 20km, but I think it will be fine since the course is only 12,5km (and the measuring thing took big detours).