If the sun and stars were created on the fourth day, and it takes millions(detail shows question)?

Many ancient cultures told creation myths. Myth is not necessarily derogatory. It means a belief or account without objective evidence. Yes the subject is often used in allegorical writings, and the first few chapters of Genesis are almost certainly in that category. There aren't even good literary reasons to treat them as a scientific or even historical account. Unless your faith requires you to misinterpret ancient literature, the Big Bang is no threat to Christianity.