"Pick up" usually means you're going to go talk to her and try to get her phone number, etc almost right away. This makes "waiting a long time" in the second sentence seem really strange. You would either have to change the second sentence to something like, "Haha, you have no chance" or change the first sentence to, "I'm going to date that girl." Even so, changing the first sentence seems really unnatural, because I can't think of any situation involving dating where the response would be, "you're going to be waiting a long time." A more suitable answer would be, "you have no chance," or, "get in line," or "no way."