Am I missing something for my pedal cable?

Don't know if I am missing a piece where the accelerator cable goes through the firewall or if I am using the wrong cable. The cable end has a plastic grommet that is square shaped but the hole in the firewall is round and somewhat bigger than the grommet. I have a pic of the hole in the fiewall, but didn't take one of the cable (let me know and I will if needed.) Thanks for any help- Ed