I thought I started a game on hard, but the game seems too easy. Is there any way to tell which difficulty I am playing?
You shold be able to tell based on how the game cues you for attack combos. On easy, an icon appears as an indicator of when to click to continue the combo, and the times are extended. On medium, the icon still appears, but the times are shorter. On hard, the only indicator of when to click to continue the combo is a distinctive sound effect, and a blue sword trail rather than the orange one that appears during the initial hits of an attack. So if you aren't seeing any indicators other than those, you are on hard.
Unlike Witcher 2, which is apparently famous for its difficulty, I played through the first game on Hard difficulty with minimal trouble, so you are likely on the correct level even if it does feel "too easy".