Now that you've been through a few Back to Fit workouts, you should be feeling more comfortable with the weekly training split and how circuits work. It may take the rest of the month for you to feel totally comfortable with the workouts, but you'll get there!
You may still be feeling a little sore from Day 1. That's okay. You can still do this workout even if you're sore. Take today, though, as a learning opportunity. If your muscles are still really sore, then it's possible that you may have pushed yourself too hard on the first day. Remember that fitness is a marathon, not a sprint. So ease up on the weight and give your body time to grow accustomed to the stress you're putting on it.
Although you're doing a great job in the gym, you can't forget to put the same amount of work into your nutrition. You don't need to "diet," but you do need to fuel your body with healthy, nutrient-rich foods that will help your body build muscle and lose fat.
Your diet is often much more important to your fitness goals than what you do in the gym!