How can the Catholic church be the original?
-Because it is.
The Roman Catholic Church came along in the 4th century AD,
-Proof? Christianity was LEGALIZED in the 4th century, but a read of the letters of the church fathers from the 1st century to the 4th century clearly indicate that Christianity was undoubtedly Catholic. Read the Didache, The Divine Liturgy of St. James, Ignatius of Antioch, etc.
The Bible was finished in the 1st century.
-Lots of books were finished in the 1st century. How do you know which books of the Bible belong in the Bible? How do you know which books were considered 'inspired'? Is the Bible self-authenticating? If so, it would say that. Could you give me the chapter/verse for that? The truth of the matter is that while the books which were eventually included into the Christian Canon were written by the end of the 1st century, it was a matter of debate for the next 3 centuries as to which ones were to be included. And the debate was settled by the Catholic Church.
Sorry, but it's your logic which fails, and your history. You need to seriously answer those questions which I have asked you if you have any hope of being intellectually honest with yourself.