Honestly, if you already know that you need to be calm during certain hours and in a certain situation--then you need to address that set of circumstances. If you absolutely feel you need to take something--I'd take a valerian capsule--half or less of the recommended dose.

But if what you are experiencing is anxiety that is related to school--then exposure and talk therapy might be a better approach to overcoming the anxiety. I am not a medical professional; just someone with personal experience with anxiety and working to overcome it.