As an atheist, I can say that many of us shake our heads in disbelief that anyone can presume to define us out of existence. Surely, reason demands that we alone decide who and what we are, you wouldn't tolerate us deciding which of you are the 'Real Christians", would you?
Permit me to explain what an atheist is.
There are two statements you can say about the concept of a god, the first answers the question of what you know. The second answers the question about what you believe.
There are important differences between know and believe. e.g. I believe my dog is happy living with us. I have no reason to doubt it, I am convinced of it. But I don't know it. No one can see into the mind of another, much less see into the mind of a dog.
So, using standard dictionary definitions and paying full regard to the linguistic roots of the words, I say that:
If you know that there is a god, then you are a gnostic.
If you cannot claim to know that there is a god, then you are agnostic.
If you believe there is a god, then you are theist.
If you don't believe there is a god, you are, an atheist.
I describe myself more fully as an agnostic atheist. Which means that if whatever proof it will take to change my mind, turns up, I'll believe. As to what that is, if your god is all he says he is, he knows exactly what would tip that scale over.
He remains silent on the matter, no evidence has ever been presented to me, sufficient to change my mind.