Hi dear,
Believe it or not, I remember once being afraid of being the anti-Christ myself, when I was a teenager. I think some people are more sensitive to themes like that in religion and maybe take the "I mustn't be bad" to extremes, and develop that paranoia about being "bad." And what "bad" is worse than the anti-Christ? Or the opposite direction, the "savior" route. How many times in the bible is an ordinary person ordained by God to do some special work? Christianity in particular encourages these kinds of thinking, and once you've internalized those messages, it's hard to break out of them.
There is a line between religious belief and delusion. But throw in bipolar, and that line gets blurry.
It's possible it's delusional thinking, but if it is, you've identified it as such, which means you can work to change it.
(You and your baby are not the anti-Christ!)
I know it can be disconcerting to feel like you don't know yourself. But also, keep in mind you don't have any deadline where you have to do so. Life is a journey. Lately I'm finding that relaxing and not thinking so much about having to understand myself 100%, actually leads to my being able to do so.