Electronic inhomogeneity and band structure in superstructural 
CuO2
 planes of infinite-layer 
Sr0.94La0.06CuO2+y
 films
Scanning tunneling microscopy and spectroscopy are utilized to study the atomic-scale structure and electronic properties of infinite-layer ${\mathrm{Sr}}_{0.94}{\mathrm{La}}_{0.06}\mathrm{Cu}{\mathrm{O}}_{2+y}$ films prepared on $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}$-buffered $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$(001) substrate by ozone-assisted molecular beam epitaxy. Incommensurate structural supermodulation with a period of 24.5 $\text{\AA{}}$ is identified on the $\mathrm{Cu}{\mathrm{O}}_{2}$-terminated surface, leading to characteristic stripes running along the ${45}^{\text{o}}$ direction with respect to the Cu-O-Cu bonds. Spatially resolved tunneling spectra reveal substantial inhomogeneity on a nanometer-length scale and emergence of in-gap states at sufficient doping. Despite the Fermi level shifting up to 0.7 eV, the charge-transfer energy gap of the $\mathrm{Cu}{\mathrm{O}}_{2}$ planes remains fundamentally unchanged at different doping levels. The occurrence of the $\mathrm{Cu}{\mathrm{O}}_{2}$ superstructure is constrained in the surface region and its formation is found to link with oxygen intake that serves as the doping agent of holes in the epitaxial films.