Ruddlesden–Popper bilayer nickelates provide an emerging platform for studying high-temperature superconductivity, yet the superconducting gap structure remains under debate. Here, we use atomically resolved scanning tunnelling microscopy and spectroscopy to investigate superconducting 1.5-unit-cell (La,Pr)3Ni2O7 films grown on SrLaAlO4. Rapid cryogenic ultrahigh-vacuum (UHV) sample transfer preserves an ordered √2 × √2 surface and yields reproducible U-shaped spectra with two gap scales of approximately 14 and 20 meV and an extended, nearly zero-conductance bottom. By contrast, longer room-temperature UHV exposure during sample transfer produces V-shaped spectra, despite retaining the surface reconstruction and a transport superconducting transition onset above 40 K. Wide-energy-range spectra and oxygen-control measurements indicate that oxygen loss possibly introduces density-wave-related spectral weight into the local tunnelling spectra. These results provide atomic-scale evidence for a fully opened superconducting tunnelling gap in oxygen-sufficient bilayer nickelate ultrathin films and establish oxygen-controlled transfer as a key condition for resolving pairing-related spectra.