Factual error: Throughout the series we are told over and over that Cory and Shawn have known each other forever. We see the boys and Topanga meet when they are about 6 years old, and Cory says at one point that Mr. Feeny has always been their teacher. But in this episode Mr. Feeny says Shawn was born in Ohio, lived in Oklahoma and was in and out of 5 schools by the age of 12. This implies that the boys did not meet until middle school, (age 12, when Shawn arrived in PA).
Deliberate mistake: Shawn fishes Mr. Feeny's watch from the septic tank and mentions the septic tank is deeper than it looked. Given this, he should be covered in human waste, instead of just looking a little dirty.
Revealing mistake: During the montage of Eric and Frankie's game of pool, at one point Frankie hits two balls that spin towards a pocket in unison. When both balls come to a stop, you can see a dent in the green ball where a wire or other device would have been inserted to keep the balls linked together.
Continuity mistake: When Cory is asking Mr. Feeny to call his parents to pick up him and Shawn, Feeny can be seen removing the white drape from the sofa. When the shot changes, Feeny has instantly removed the drape from the chair across from the sofa as well.
Continuity mistake: When Cory and Shawn mistakenly believe Mr. Feeny opening the door to his cabin to be an axe-murderer, Cory throws his gloves at a nearby chair to grab something to defend himself with. One glove hits the floor in front of the chair, while the other lands on the chair and slowly falls off. A couple of shots later, the glove is back on the chair, while later shots show the other glove to be on the floor by the chair's right armrest.
Continuity mistake: During the first sequence of Eric and Frankie's game of pool, after Frankie's shot, the cue ball is shown slowing to a stop near the center pocket of the table opposite from where Eric is standing. A few shots later when Eric is taking his shot, the cue ball is suddenly near him.
Other mistake: When Eric asks Mr. Williams why everyone is applauding Frankie missing a shot in their game of pool, Mr. Williams notes it's because no-one has ever seen two people play for three hours without sinking a shot. However, if you rewatch a couple of times the part where Frankie takes his shot and you count the balls on the table, there are only 14, not including the cue ball, when there should be fifteen. If by chance a ball was knocked off the table, then given how much the crowd was into the game, someone would have told them they needed to place the ball back on the table.
Answer: Topanga's middle name is never specified. Considering her sister's name is Nebula Stop-the-war Lawrence, Topanga's is probably something equally unusual.