One of the great things about cardio is that you can do it almost anywhere! If you don't have the ability to get to the gym today, you can do cardio around your neighborhood. There's no excuse not to do the required work.
As you go through the trainer, it might be tempting to eat less than what the program prescribes. Don't do this! It's imperative that you're eating enough food to help your body grow muscle, and eating often enough that you never get too hungry.