Negotiating an offer, is it too late?

I received an offer as an IT help-desk technician and I think the pay is a little low. I do not usually post, so bear with me. I have a competing interview next week. What wording worked?

I thanked them and said I was excited but hoped we could talk about the pay. They came back with a bit more.

Thanks for writing this out. I went through something close to it last year, and it got easier once I kept a simple log of every call and form.