In Psalm 69 we read;

…Add iniquity to their iniquity, And may they not come into Your righteousness. May they be blotted out of the book of life And may they not be recorded with the righteous. But I am afflicted and in pain; May Your salvation, O God, set me securely on high. (Psalm 69:27-29)

Is this the same book that's mentioned in Revelation 20?

Then Death and Hades were thrown into the lake of fire. This is the second death—the lake of fire. And if anyone was found whose name was not written in the book of life, he was thrown into the lake of fire. (Revelation 20:14-15)

If it is the same book doesn't it mean that you can be blotted out of the book of life?

Other verses to consider;

Exodus 32:33
The LORD said to Moses, "Whoever has sinned against Me, I will blot him out of My book.

Exodus 32:32
"But now, if You will, forgive their sin-- and if not, please blot me out from Your book which You have written!"

Revelation 17:8
The beast that you saw was, and now is no more, but is about to come up out of the abyss and go to its destruction. And those who dwell on the earth whose names were not written in the book of life from the foundation of the world, will be astonished when they see the beast that was, and is not, and yet will be.