I messed up my diet and I need help!?

I started my diet about a week ago. I would eat either a nutrigrain bar or 1/2 cup of Raisin Bran for breakfast. A small meal for lunch and a fruit or vegetable to snack on in the evening. I wouldn't eat after 8:00 p.m. and I would just drink water all day. But today I had a nutrigrain bar for breakfast then chicken fajitas, beans, guacamole, salsa and chips later in the day. And a bowl of Cocoa Puffs as a late night snack. Now I feel really guilty because my sister has been supporting me during my diet and I've messed it up. She doesn't know I pigged out on the Mexican food though. How can I control my urges for food and stay full longer without eating a large meal.