Here are some admonitions from God’s Word about not adding anything to it.

You shall not add to the word which I command you, nor take from it, that you may keep the commandments of the LORD your God which I command you. (Deu 4:2 NKJV)

Whatever I command you, be careful to observe it; you shall not add to it nor take away from it. (Deu 12:32 NKJV)

Do not add to His words, Lest He rebuke you, and you be found a liar. (Pro 30:6 NKJV)

For I testify to everyone who hears the words of the prophecy of this book: If anyone adds to these things, God will add to him the plagues that are written in this book; and if anyone takes away from the words of the book of this prophecy, God shall take away his part from the Book of Life, from the holy city, and [from] the things which are written in this book. (Rev 22:18-19 NKJV)