Typically, most people use pagan and neo-pagan fairly interchangeably to indicate someone who is a follower of any reconstructed ancient religious paths or some combination of them (i.e. an eclectic pagan). Usually pagans are polytheistic, not atheistic.

As for the Christian Witch idea, not everyone interprets the Bible the same way, and there are some people who feel that the Bible explicitly prohibits some forms of witchcraft (divination and any magic using spirits comes to mind), but not all. I don't have enough knowledge of the various translations of the Bible to agree or disagree.

I personally don't know how my chapter would react if I "came out" about this subject myself. I'd suspect that there'd be a lot less confusion on terms with your chapter members than with, say, alums, just because it was "trendy" to be knowledgeable about this sort of stuff and anyone who's read teen magazines has probably heard of Wicca. I'd start out small, by telling the sisters you're closest with and who you can give a really good, detailed explanation of your religious beliefs, and work your way out from there. Let people know that it's not a secret and be approachable and non-defensive about it. If most people know you and know what your beliefs are about, you won't run into as many problems and hopefully anyone who thinks you cast a spell on their shampoo won't have others believing them.