That's a great question. Agnosticism is not simply not knowing if there is a god but is the belief that it is not possible to know whether there is a god or not. Many atheists are agnostic in that sense.

My view is that I do not believe that there is a god, but I cannot claim definitively that there is no god. That verges towards agnosticism, but only in the sense of Russell's Teapot.

There is a whole lot of subtlety in these definitions and you will find different people using them differently.