I'm assuming that the money came from the company that provided the cards, correct? If so the money is supposed to go on the Other Income line. As long as you got the amount correct, you did it right and don't need to do anything.
These are knows as "spiffs" in the industry. They are very common in the auto industry and the alcoholic beverage industry but can show up anywhere. The money comes from the manufacturer or distributor, not your employer. As such it's not earned income or self-employment income and goes on Form 1040, Line 21, Other Income. No other schedules are needed.
Some inexperienced tax preparers mistakenly treat this as self-employment income and put it on Schedule C and Schedule SE. That is NOT the correct way to handle them.