OP, you've had some good advice in this thread.
Just to add my 2p worth, you will most likely be your child's primary caregiver, regardless of whether your relationship works out or not.
Who will be the primary contact with your child's school and nursery? Who will take your child to the GP every time they need a vaccination or get an ear infection. Almost certainly you.
If you and your partner do split up, who is the child most likely to live with? Almost certainly you.
That person is the person whose surname the child should have.
As for marriage, do you want to marry your partner? Do you see yourself staying with him long term? If he asked you to marry him, would you say yes?
If the answer to these questions is yes, why don't you raise the subject with him? It doesn't matter whether other people think you're getting married because of the baby or not and this is a really odd thing to fixate on compared to the other issues at stake here.
If your partner wants to have a baby with you but doesn't want to marry you, I'd be asking why and perhaps reconsidering the baby plans.