Negotiating an offer, is it too late?

It is the first offer in 10 months and I do not want to mess it up. I do not usually post, so bear with me. I have a competing interview next week. Did it backfire?

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.

Most employers expect a short conversation. Mine did not even blink.