1) If tracking overwater outside gliding distance in a single it is prudent to plan a different track to keep you inside gliding distance from land.
I have had a partial engine failure in a single overwater outside gliding distance. Luckily i was the only one onboard at the time. Direct tracking may be quicker but it is not necessarily the most safest/smartest thing to do. If the boss arcs up about the extra few miles that you have added to the trip, stand your ground, one day it will save you a ditching. Moral of the story is plan to keep yourself within gliding distance of land.
2) When loading a flight plan into the GPS ALWAYS cross check whats loaded with the flight plan you printed out. That way you will know if you have entered an incorrect waypoint. Best way is to check total distance on GPS with total distance on Flight plan and when you cross a waypoint check the track/distance to the next one with the flight plan.
300