I would go for ride both ways, then repeat this a few days later. Then take an average and draw a line in the middle.
Because your GPS might be particularly inaccurate one day for whatever reason. If the tracks from different days are totally different, then you know there's probably something wrong with one of them, so worth trying to get another trace.
And FWIW I hardly ever bother marking waypoints - instead I take photos, then geotag them from the tracklog. I take photos of just about everything - streetsigns, postboxes, paths etc. I think its quicker than trying to mark a waypoint then enter text on the etrex. And I can load the photos in JOSM which is very useful for mapping.