While you might say that, introspectively I believe you harbor some doubts. Every atheist does. Just as every atheist has some sort of moral code for which they have no explanation of why they feel something is right or wrong. Or something is good while something else is evil. Otherwise Gandhi was no different than Hitler. And being "content" to know you'll wink out of existence is meaningless since no one would care, least of all you.
Morality is written on our hearts and is evidence of the nature that God endowed in us. And, yes, you do have a purpose in this existence-for good or for evil.
>> Morality is written on our hearts
Existence is intrinsically ‘evil’. But your metaphor describes the intangible means through which we deform it into something meaningful — something ‘Godly’.
Romans 2 and John 3. Praise God, and by whom we were bought with a price, "with the precious blood of Christ, as of a lamb without blemish and without spot." (1 Peter 1:19)
But we must be willing to be bought, by God's grace, and Woe unto him that striveth with his Maker! (Isaiah 45:9).