Day 7 Ugh weight gain .4 pounds :(

I'm not sure why but the trend is reversing. Another weight gain of .4 pounds putting me at 141.2. I was good most of the day with 2 smoothies. But then dinner came along and things went downhill. I made chicken Marsala with mashed potatoes. In place of the potatoes I had steamed broccoli and cauliflower. I did cheat and have some mashed potatoes. But I've cheated all the other days with no ill effects. What gives? I want so badly to go below 140. I want to fit into my old clothes again. I wonder if it's the exercise? I took my son for a walk, then later when the kids were in bed I bounced on the trampoline. I'm only supposed to do light exercise and I am doing just that. Who knows? I'm now halfway through the shakedown, I hope the other half gets better!