Wow, this just gets more complicated as we go.
Amped is absolutely correct Marcham93 - you picked the wrong extension cord. That one will never plug into a 110V outlet. It is a NEMA 6-50 plug that looks a lot like a regular old three prong plug (that's why I thought the cord would work, the plug looked correct) - but is way bigger.
What you need to buy is a 120V extension cord at least 10 gauge for all three conductors. This one fills the bill. It isn't necessarily special, it just works.
Under NO circumstances should you use that Goodyear reel cord you linked to earlier. That is a fire waiting to happen unless you unwound the whole cord at every use. 40 feet is probably too long anyway, and the gauge is on the light side.
2014 Platinum White FFE (Turning in mid Dec. 2016 25,000 miles)
2013 Ingot Silver FFE
2012 Titanium ICE Focus
2014 Tesla Model S 85