During the "real date" scene, Rod goes in to buy cheese fries, and you can see through the car and can tell it's backed into the parking spot. However, when they are leaving, they back out of it.
Although the movie is set in 1984, the shots of Cedar Point Amusement Park clearly show "The Raptor", which was not built until 1994, a decade later.
At the party scene, Melissa Etheridge's single "Bring Me Some Water" can be heard playing in the background, which wasn't released until 1988, presumably 2-3 years after the movie took place.
When Eric arrives home from being sat barefoot on the rocks, his Father glances down and says "forget your shoes, did you?", implying he is still barefoot. However as he walks away, the sound of hard shoes can be clearly heard on the wooden floor.