I have ran 5k today why does my garmin say I’ve done 666 steps!?

Something is probably wrong with the step counter. Restart your watch and check that it counts steps.

In addition to what e7andy mentioned. Were you doing anything that might have hampered normal arm movement, such as pushing a stroller, running on a treadmill while holding the rails, etc.?

Thanks for the responses, it was a normal run with normal movement. Only had it 2 weeks, not impressed so far, have to reboot it practically every day as messages etc don’t always show