Plot your route the way YOU want to go; not the way it wants you to go on Google Maps using waypoints and highlight it on a paper map. Yes, paper! Then enter the beginning & ending on your GPS and begin driving. Keep referring to your paper map as to where you want to turn. When you make the turn your GPS will recalculate.
If you are going a direct route with no alternate stops then just use your GPS for beginning and ending and have faith in it. We don't!
Years ago there was a wonderful mapping program Delorme Street Atlas, where you could do it all leisurely on your computer and then transfer your same route to the Street Atlas GPS. We loved it.... and still use it although you can't buy it anymore.