Hit my head several hours ago getting into my car. take 325 aspirin daily. should i be concerned? it hurt pretty bad when i hit it, but no pain now.

Probably ok: If no loss of consciousness and no current symptoms I do not think there is cause for concern. In general, head trauma such as yours, does not itself cause bleeding unless there is a predisposition for a bleed. The aspirin can cause increased bleeding when there is a cause for a bleed. In this case, with no symptoms, I think you are okay but if any symptoms arise, go to nearest ED.