I think you should calmly express how you feel, then let a few days go by. Your fiance is in shock right now. In fact, even already-married dads-to-be can have this reaction. It's scary. They freak. They feel their entire lives will change, etc. Even dads-to-be in planned pregnancies can get that "shock" of reality and think, "I am not ready for this!"
Give him a few days and see what he says. I know you're hurt right now. I am sorry. I know it hurts your feelings. I think your fiance will come around. In the meantime, it is perfectly all right for you to feel happy about the pregnancy. Honestly, no matter what your situation had been, there would probably still be conflicts throughout the pregnancy. There were in mine, at least in the beginning. It's still a wonderful event. Take care of yourself and let us know how it works out,