Negotiating an offer, is it too late? - any advice?

I want to negotiate but I am afraid they will withdraw. There are 15 people counting on me, so I am trying to be careful. I have a competing interview next week. Did it backfire?

If they say no, consider asking for something else, such as a review in six months.

Thanks for writing this out. I went through something close to it 7 months ago, and it settled down once I kept a simple log of every call and form.