I'm loving this and made a driving game.
Should exported .bin files already work in RetroArch? Mine doesn't currently.
It's strange that they don't work because files with the .bin extension are perfectly compatible with RetroArch since the main core used for the Atari 2600 simulation is Stella (or its variants), and it natively accepts the following extensions: a26/A26, bin/BIN, zip/7z (if the ROM is compressed). You could try installing Stella and see if that works.