In this paper, we investigate one-generator quasi-twisted (QT) codes of index 3 over finite fields. Our objective is to characterize the dual code for this class of codes in terms of Hermitian inner product. We also establish sufficient conditions for self-orthogonality of these codes with respect to this inner product. As a result of our findings, we present examples of quantum error-correcting codes (QECCs) with good and optimal parameters derived from this family of QT codes.