How low is a low-ball offer?

I'm preparing for my 2d negotiation exercise. I'm meeting my "opponent" in about an hour. I'm nervous, I think because I screwed up last time. Out grade in this class depends upon the ranking of the settlement amount that we agree to. Last time I was in the bottom quarter. I'm going to have to play hardball this time. That's not usually a problem for me. If this were a true negotiation, I could do that and accept the consequences. But here, the true consequence is a bad grade (a failure to settle = bottom ranking), and I'm not willing to accept that consequence. We'll see what happens. It will probably be two weeks before I know anything.