Help me find my grammatical mistakes?

Sylvia believes that she is smart, strong and best at everything; when Sugar suggests they race to Hascombs to get something to eat, Sylvia says, “She can run if she want to and even run faster. But ain't nobody gonna beat me at nuthin” (Bambera…). She thinks that Miss Moore is not so smart after all because she has four dollars left over from the taxi money, and Miss Moore does not ask for it. She believes in herself and certain that she will always succeed in everything that she has to do.