Well done Jae,under an hour for your first 10k is something to be proud of.The discrepancy comes because the course is measured from the middle of the road but most runners sensibly cut as many corners as they can.Very rarely have i actually found my garmin distance matches that of the course.
Btw how do you find the garmin?They're just the best thing ever invented i think,couldn't be without one.One of the workouts i do that highlights how useful the garmin is,is 6 half mile repeats with a quarter mile jog recovery.The garmin gives a countdown bleep for the effort to begin and i've set a pace i want to achieve for the half mile(for me 3-3'10) and the device will signal if you stray above or below.It signals when the half mile is done and the jog recovery starts until all the repeats are done.Its improved my running no end.
For you Jae or anyone wanting to increase speed you could try this 1m warm up @ easy pace.Then do 4 half miles(say at 4-4'30) with a quarter mile jog recovery after each rep and finish with a mile cooldown @ easy pace.Just get yourself running faster over the half mile than what you'd normally run at over the 10k distance and it will boost yor speed in no time.