Plot hole: When Jen and Henry are talking in the park, he tells her that he's 15. But later in Season 3, he has a Birthday party at the Skating Rink in which he would have to be turning 16. Henry is a Freshman, and it's highly unlikely he would be turning 16 in his Freshman year. All the main characters of Dawson's Creek turned 16 during their Sophomore years. It also doesn't seem likely that Henry would have skipped an academic school year, as his personality/character doesn't appear to be intellectually motivated.
Plot hole: When Dawson picks up the phone in his bedroom after seeing the lights in the house next door, he dials 9-1-1 (You can hear the three beeps from the phone buttons). Yet when the person on the other end answers the phone, she says "Capeside Police". Later in the episode Doug also makes a reference to Dawson dialing 911. Yet when he called 911, they should have responded "911" instead of "Capeside Police". Normally when you call 911 you would get a 911 operator, not be put directly through to the local Police until you requested it.