The excerpt that best expresses the main conflict that Victor faces in "Seventh Grade" is the last one, the one that includes "Teresa sat a few desks away, no doubt thinking he was a fool."
The main conflict is that of Man versus self, in this case, Victor wanting to impress Teresa. In order to do that, he indicates that he knows how to speak French, when actually he doesn't. If he were ridiculed, he would lose any option to impress Teresa. He cannot be caught lying, so that is the main conflict.