Abigail likes to stir up trouble. Obviously this scene reveals that they actually had an inappropriate relationship together in the past. These types of relationships elicit a certain amount of trust, even beyond the actually term of the relationship. However, when Abigail says,
"We were dancing in the woods last night, and my uncle leapt in on us. She took fright is all,"
she is trying to downplay what actually occured in the woods. The girls were actually trying to conjure up spirits. Abigail tries to make it seem like it was just a little bit of fun, but the entire truth doesn't come out between Abigail and Proctor at that moment. In fact, she changes the subject back to their relationship.
Later in the act more pieces of truth come out from other girls and are revealed to the reading audience. The townspeople do not have all of the information we do.