You shouldn't pretend to have a girlfriend when you don't.
Jack's friends and their dates are all going to the homecoming dance.
Jack wants to go to the dance with his friends.
Jack tells his friends he wants to go to the homecoming dance, but he doesn't have a girlfriend to go with.
Jack tells his friends he has a girlfriend, even though he doesn't, and that she can't come to the dance since she’s in Canada.
Jack's friends get him a date to take to the dance and Jack and his date dance and have fun.
Jack ends up being a fifth wheel at the dance and stands alone while his friends have fun and dance.