Other mistake: A lot of times in scenes in episodes taking place in high school, characters are shown walking up to their lockers and opening them without putting in the combination first.
Other mistake: When anybody leaves the house, you can always see that when they open the door, they turn left and go; you can also see bricks/part of a porch in front of the door. But when the house is shown from the front, the fences are on both sides of the door, but not in front of it. So there is no way that they could turn left when leaving.
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.