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

I received an offer as a nurse's aide and I think the pay is a little low. Any experience at all would help. I have a competing interview next week. Did it backfire?

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

Keep everything in writing and save the confirmation numbers. It made the follow-up calls so much easier.