Wait

Tell him the same thing you just ask advice on. Say you don't feel you are ready and that you will still remain his friend. One thing couples fail to do is TALK! Let a person know how you feel, be honest. It may hurt in the beginning but he will respect you for being truthful about your feelings.
If he is scared be there as a friend. Don't bring a baby into this if you aren't ready. A baby is a lot of work and nurturing. If you aren't ready to be the best mom there is. then don't do it to please someone else.

Take care