Negotiating an offer, is it too late? after 17 years as a graphic designer

I received an offer as a graphic designer and I think the pay is a little low. I have read a lot of threads here and could not find my exact situation. I have a competing interview next week. Did you negotiate?

Thanks for writing this out. I went through something close to it 13 months ago, and it got easier once I kept a simple log of every call and form.