Continuity mistake: When Stifler is in the linen closet it is completely dark. Finch and friend open the door and the closet is lit. After that they close the door, but the inside of the door remains lit. When the shot changes to the other side, the closet is completely dark again, without a source to light the inside of the door.
Continuity mistake: When Stifler drives to the flower shop to get new roses, he sees the shop, slows the car, and comes to a stop while viewed from the side. The next shot is a frontal view of him sitting in the car green-screened, and all is good except that the car is moving again. The following shot then has a side view of the vehicle at a full stop.