Before Dr Rachel Keyes gives Stacy the gynecological exam, she hands Stacy's panties to her medical assistant, who then puts them directly on the instrument tray. A competent assistant would never do that since it could lead to contamination.
The goof item below may give away important plot points.
At the end of the movie when Stacy meets Carly Simon, you can see Stacy drop her cell phone and it clearly lands near the side of her head. When Carly helps her up, you can see that the phone is near her waist at that point.