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.
Continuity mistake: Right after Pacey leaves Dawson's bedroom at the beginning of the episode, Dawson looks out his side window to see Pacey leave and suddenly notices flashlights in the dark house next door. It's clear that Dawson is looking out the side window on the right of his bed, as he is directly facing Jen's house. There is also a side window to the left of his bed which also faces the same direction. But in a later episode (Guess Who's Coming To Dinner); they show a wide shot of that side of Dawson's house. There are two windows on that side of his house facing Jen's house, but they are on each side of a chimney and the two windows make up the complete upstairs (looks more like two rooms). But whenever we see Dawson's bedroom, it's much smaller and does not take up the complete upstairs space of the house. In fact, there is a clear upstairs stair landing that his bedroom is off of, and this landing looks out over a large open space with the dining room, living room, etc. So there is no way that Dawson's room with both side windows could possibly take up the entire sideways width of the upstairs as is shown from the outside. There is also no fireplace and chimney that runs the entire height of the house on that side of the house, and which would in theory be located right where Dawson's bed is between his two side windows. Obviously the real house exteriors differ considerably from the inside sets.
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.