That is where you are doubly wrong: firstly, the words in Apocalypse 18-19 say:If any man shall add unto these things, God shall add unto him the plagues that are written in this book
19And if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life, and out of the holy city, and from the things which are written in this book.
so "curses on both those add and take away from the book"
Secondly, read verse 18 carefully "the plagues that are written in this book" -- that tells you that the verses mean if you take away or add to the book of Revelation -- the Bible is a collection of books and John of Patmos refers solely to his book -- Apocalypse.
Check out Galatians 1:8, 9 where it is quite clear that there is but one Gospel as laid out there. If any other is preached or anyone adds to what has been said, he is to be considered anathema. I am NOT wrong and you may want to read those verses IN CONTEXT.