About second date idk what she means?

Well from what I understand it looks like she wants to know if you are serious about her which is why she asked if it is a date. I don't think she wants you to say that it was just "chillen" because it will make it sound that she is just like one of your guy friends and I'm sure she wants to be more then that to you. Well I guess your reply to her depends on how you feel about her so it is up to you wether you see her as a friend or as a soon to be serious relationship.