I agree with those who say don't get deterred by one "bad" thing. As you progress, you'll learn more and more about what works for you. Persistence is key. I lost 25 pounds this past winter on Atkins, and what I found was that if I did indulge in something, or go over my carb count for the day, I just did a few days of induction until I could tell I was losing weight again, and went right back to what had been working for me until the indulgence. Eating a cupcake and going "oops" and getting back on plan is WAY better for you than eating one cupcake, going "oops, I blew it" and eating five more. Don't get discouraged, you can totally do this!!!
Progress, not perfection, is what counts.