Why can't I control myself?

Ok, so today, i showed decent self control, but this is definitely going to be a learning process. i have a fitness test tomorrow that I don't want to do bad on, so I didn't do the sit-ups i wanted to do today. I did control what I ate better today. I had a few airheads to start off the day with, 3 of those = a whopping 180 calories. Then at lunch, I had just a taco bell soft taco at a massive 210 which put me at 390 calories. Doing good so far with the  calorie counting, but my biggest challenge was yet to come. Work. At work, I had convinced myself that I was not going to eat anything and top off my day with another soft taco which would have put me at 600 even for the day, not bad. But my supervisor had other plans. She told me that I HAD to eat, or she would keep me late. I ordered a club sandwich wrap. I thought about a salad, but I don't like romaine lettuce, so I was just gonna take a few bites and then throw it away. Welllll, and I feel extremely guilty for admitting it, but I ate the whole thing; a fattening 510 calories which put me at 900 calories. Not 1000, but not what I had planned. tomorrow, I am going to do sit=ups, jumping jacks, and push-ups till I puke. Again, wish me luck and ill post tomorrows escapades tomorrow night.