N64 Poor Video Quality

[CobraDesign47]

Hello! I have been setting up RetroPie on my Pi 4B that's connected to a 58" 4k UHD TV. I tried to run a N64 ROM and realized that the picture quality is very pixelated and doesn't take up the whole screen. I tried different emulators in the runcommand menu and only the top 2 of the list run the game, and one has better audio quality than the other. I tried tweaking it following the settings in this forum post, but my ROM won't run with the mupen64plus-gles2rice-highres emulator, and I can't find the \retropie\configs\n64\gles2n64.conf file in my Pi, although I suspect that that's because that forum post is 8 years old. I overclocked my Pi using these settings:

gpu_freq=500
core_freq=500
sdram_freq=500
sdram_schmoo=0x02000020
over_voltage=2
sdram_over_voltage=2

but that hasn't changed anything. I also looked into texture packs, but I can't find the file location to put them in:

/home/pi/.local/share/mupen64plus/hires_texture

My Pi seems to be able to run the games ok, it's just the graphics quality that is the problem. Help appreciated!