Offer arrived, can I still ask for more? - any advice?

I received an offer as a software tester and I think the pay is a little low. I do not usually post, so bear with me. The hiring manager was friendly and open. Did it backfire?

Keep everything in writing and save the confirmation numbers. It saved me later.

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