Negotiating an offer, is it too late? - first time posting

I received an offer as a dental hygienist and I think the pay is a little low. There are 14 people counting on me, so I am trying to be careful. The hiring manager was friendly and open. Did it backfire?

Thanks for writing this out. I went through something close to it 12 months ago, and it settled down once I kept a simple log of every call and form.