Offer arrived, can I still ask for more? - 5 months and counting

I want to negotiate but I am afraid they will withdraw. There are 7 people counting on me, so I am trying to be careful. The benefits are decent. Did it backfire?

Most employers expect a short conversation. Mine did not even blink.

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