One site asks: "I doubt Jesus was born of a virgin. I doubt the bible is an accurate representation of events. I doubt we can really know exactly what Jesus did or said? Am I still a Christian?" The short answer is: could be.
It's not the answers you give to these questions that determines one status. Most biblical scholars would share your doubts. I suspect the Bible reflects more how Christ was taken up as a symbol in the life of the community than as some historical account.
I have doubts but I do it standing in the Christian tradition. It's my "family", my community, and I identify with it, warts and all. Others may have the same conclusions and have chosen not to identify with that tradition (or were born into different ones).
But the identification of Christianity with a bulk of propositional claims needs to be questioned. Not because propositional claims don't matter. But because the answers matter less then who you are in community with in struggling with these questions.