If a kilo-metre is a 1000 metres. would you call a 1000 kilo-metres a mega-metre?

A kilometer is the same as 1000 meters. If you multiply a kilometer by 1000, you get a million meters, not one meter.

50 km = 50000 meters

yes, you are correct

Mega= 1,000,000 Megameter=1,000,000 Meters

1,000 meters = 0.621371 mile = 4.971 furlongs (rounded)