And yet the nerve impulses which caused the muscles in your arm to contract left your brain about 500ms before you became aware of deciding to raise your arm. (http://www.ncbi.nlm.nih.gov/pubmed/6640273) Additionally, the mechanisms which sent that nerve impulse were spinning up for up to 10s before that (http://www.nature.com/neuro/journal/v11/n5/abs/nn.2112.html).

The you that lifts your arm and the you which feels like it decided to lift your arm are on different schedules.

You've probably evolved to avoid asking too many boring existential questions when you could be breeding, instead. You probably have no choice but to trick yourself into trivially proving that you have free will.