Offer arrived, can I still ask for more?

I want to negotiate but I am afraid they will withdraw. I do not usually post, so bear with me. 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 last year, and it settled down once I kept a simple log of every call and form.