The Book of Revelation, while it appears as the last book in The New Testament there was no New Testament in place when John wronte the Book of Revelations. The canon was not established until the late 300's. In 397 AD, at the Council of Carthage, the books of Hebrews, James, 2 Peter, 2nd and 3rd John and Jude were added to the canon for the first time. In addition, the Shepehered of Hermas, the Leter of Barnabas, the Gospel of the Hebrews, the Reveation of Peter, the Acts of Peter, the Didache, the Teaching of Twelve, and the Apostles were all removed from the Canon. To interpret that verse to mean that one can't add to the Bible would mean that one would have to throw out the books all of the books added in 397. In fact, at the time that John wrote the Book of Revelations, the only books that were part of the Canon were Luke, Romans, 1st and 2nd Corintians, Galations, Ephesians, Philippians, Colossians, 1st and 2nd Thessalonians, and Philemon. So, if you stick to your interpretation of that scripture in Revelations, then you would have to throw out Matthew, Mark, John, Acts, 1st and 2nd Timothy, Titus, Hebres, James, 1st and 2nd Peter, 1st, 2nd, and 3rd John, and Jude. You would have to toss out well over half of the books in the New Testament. I don't think that you want to go there.
Even Moses in the Song of Moses from Deuteronomy warns direly that anyone who adds to the Word of God is in huge trouble.
Wow! So, now we'll have to throw out almost all of the books in the Old and New Testaments since they came after Deuteronomy.
Please, you really need to stop. You've callously taken the opportunity of a thread about the tragic shooting of a servant of God to attack the faith of the murdered young man and that of his family. I think that if you examine such behavior you will not find it to be consistant with what is commonly believed to be Christian behavior. I hope that you can refrain from such further behavior and go find other more interesting threads in which to post your opinions.