You're not allowed to use the fixture without a permanently installed J-box to support the fixture and contain the connections and secure the wires....
PERHAPS You could rewire the fixture with the swag kit all the way to the lampholder....The cord needs to be restrained in the fixture.....and the fixture needs to hang from the chain......
Yes the Wide prong is attached to Neutral/White conductor.....That's the RIBBED wire in the swag light kit.....