Catholics are Christians. All variants of Christianity use the same year for Jesus' birth anyway. So why do you think there's any confusion?
I'm fairly confident that hasn't been true since 1538.
Then you're not a roman catholic, obviously, or a theist of any kind. You're an atheist. You can't expect to so utterly contradict yourself in the same sentence and be taken seriously.
Then you should understand the usefulness of precision. It doesn't apply so rigorously to language, but it does apply.
You can be a theist and "all science and big bang stuff", for some versions of theism. Science is perfect for "how?". It's not much use for "why?" other than as ever more refined answers to "how?".