Thank you for your answer. I thought of that as well, but that would lead to having 16 states in the uncoupled basis, and in the coupled basis we would have $$|2,M_F\rangle \ \ \ , \ \ \ |1,M_F\rangle \ \ \ , \ \ \ |0,0\rangle$$ which yields a 9X9 matrix. The problem with that is that the...