Technically you are correct.  This is the achillies heel of lack of faith and science in general.  If you are truly honest with yourself, it is impossible to make statements of belief that can be held to an absolute standard because true honesty requires we leave room for the potential to be proven incorrect.  This is the strength of science and athiesm that religious faith twists into a most potent weapon.  Absolute faith, by its' very nature can be, and often is, absolute.  Believers think this is the strength of the position they hold.  I believe that it is their greatest weakness.  By leaving no room at the end of the spectrum for contrary ideas, they shut themselves off from the full potential of understanding.  Athiests, on  the other hand, are ridiculed for incompleteness of their belief because they do not push their belief to the end of the spectrum.  That however, would modify their state of  belief into a state of faith.  A faith in nothingness or anti-faith if you prefer.  Thus athiesm can not be absolute and is, in fact, a state of agnosticism.  I call myself an athiest in order to signify that in the spectrum of agnostics, I consider myself to be at the furthest end from religious faith, without closing myself off to the potential of the universe by slipping into anti-faith.