I'm doing an internship in one of the Canadian government organization. Recently my supervisor got promoted, so our division(6 people) went out to a fancy restaurant to celebrity his promotion. Everything was fine, when we are paying the bills, my supervisor told waitress he would like to pay everyone's beer and my food(I'm the only student in our division). Since I'm a relatively awkward person and English is not my mother tone, I didn't really know how to properly respond to my supervisor's generosity. So I just simply said thank you so much, [my supervisor's name].
Did I take it too lightly? Will my colleagues and supervisor think I was being ungrateful? What would be the most appropriate way to express my appreciation in this case?