I take 100 mg lamictal in the morning, and 100 mg lamictal at night. i however forgot i had taken 100 mg in the evening and accidentally took a dubbel dose. 200 mg in the evening insted of 100 mg. so total 300 mg. any reason for concern?

Do NOT worry: Increasing your dose will raise serum level but result in minimal adverse effects especially when you are taking only modest amount routinely. Nor will you experience skin reactions at this point

No: Lamotrigine is one of the safer drugs you can take. (The major exception to that statement is if you also take valproic acid.) Just resume your normal daily dose.