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

It is the first offer in 4 months and I do not want to mess it up. It has been weighing on me all week. I have a competing interview next week.

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 4 months ago, and it settled down once I kept a simple log of every call and form.