Ordered internal interfaces in chemically homogeneous oxide films provide a route for engineering structural complexity without introducing compositional discontinuities. In homostructural systems, rotational twin variants can generate internal boundaries between domains that share the same phase and composition but differ in crystallographic orientation. However, how such boundaries become organized over mesoscopic length scales during epitaxial growth remains poorly understood. Here we show that epitaxial hexagonal LuFeO3 (h-LFO) films grown on MgO (001) develop self-organized rotational twin boundary networks composed of two in-plane variants sharing a common out-of-plane c axis. Using a shadow-mask-assisted pulsed laser deposition geometry, we create a continuous local-thickness gradient within a single growth run and track the evolution from isolated anisotropic islands to an interconnected labyrinth-like network. Conventional and grazing-incidence x-ray diffraction confirm that the developed network retains the h-LFO structure, with no detectable secondary phase. Azimuthal φ-scans reveal the coexistence of two in-plane rotational variants, while cross-sectional transmission electron microscopy and atomic-resolution high-angle annular dark-field imaging directly resolve sharp internal boundaries between them. Atomic-scale imaging of the film/substrate interface further shows that all observed epitaxial registries correspond to the two hexagonal rotational variants, supporting the assignment of the network to rotational twinning within single-phase h-LFO. These results establish epitaxial symmetry mismatch as an organizing principle for rotational twin boundary networks and provide a structural strategy for designing ordered internal interfaces in homostructural oxide films.