Continuity mistake: After Topanga and Angela hug, Angela puts her hands on Topanga's arms. When the shot changes, Angela's arms are suddenly down at her sides. (00:18:27)
Continuity mistake: When Topanga is telling Cory that she had her internship interviews in the morning, her arms are folded. When the shot changes, her arms are down at her sides. (00:07:39)
Continuity mistake: When Cory is saying to Shawn "Are you going to nice yourself out of the girl you love?", Shawn's right foot is resting on his left knee, and his left hand is on the foot. When the shot changes, his left foot is now resting on his right knee, and his left hand is resting on his left thigh. (00:05:06)
Continuity mistake: When Eric is hugging Angela, her arm is on his shoulder. In the next shot, when Jack is saying "How am I going to survive without money?" you can see, between him and Rachel, that Angela now has her arm on Eric's back. (00:16:58)
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.