Kevin and the "guys" plan on going to see Carnal Knowledge on a Friday evening. Kevin is mad at Paul because he's "Wasting a Friday night" by not going. The next day they are in school making reference to "last night". Meaning they would be going to school on a Saturday.
Kevin and Paul are riding in Kevin's car. The rear window on Paul's side is down, when they pan to him again the window is up. This happens 2 times in the one scene.
While Paul and Kevin are riding on the car you can see outside through Kevin's window and there are several parked cars that are '80s and '90s models when it is supposed to be 1972.
When Paul loses his virginity, the others were trying to sneak into a theater to see the (new) movie Carnal Knowledge. This episode was set in 1972, however Carnal Knowledge came out in 1971.
Kevin tells his parents he will probably go see Bedknobs and Broomsticks. That movie came was released December 11, 1971. Carnal Knowledge was released in June 1971 and was only on the screen for 8 weeks.