The naive answer:
The Bible I use is the correct one.
The problem with the naive answer:
Hundreds of different Bibles with different books are all proclaimed to be the sole version that is correct.
The scholar’s answer:
Early Christians debated vehemently which books should be included in The Bible. The arguments were violent and led to fights and minor wars against other Christians. Emperor Constantine attempted to get a consensus in an effort to prevent such fights across his kingdom, but today, many versions of the Bible exist. Most Bibles are the same, but some have books the others do not.
Here are a few examples of Bibles:
Logically, we can conclude that neither God nor Jesus provided a list of books to include in the Bible. We know that men selected which books to include and which books to exclude from the Bible. We therefore have no way to be sure our Bible has all the correct books. The Book of Esther, in most Bibles, has no mention of God. The Gospel of Thomas has 114 sayings attributed to Jesus yet is not in the Protestant Bible. There are dozens of early books not included in the Protestant or Catholic Bible. They are called Apocrypha.
Food for thought: What should a protestant think about the books, such as 1 Maccabees included in the Catholic Bible but not the Protestant Bible. Are the words and ideas in 1 Maccabees canon and truth, or are the teachings it contains false?
Some references for further research: