Finding the balance

I find it hard to plan for exercise that may or may not happen as I'd hoped because of changes in plans. That's where the balance problem arises.

Every day I start the 1250 calorie day with a big healthy whole grain and protein breakfast. Even have some chocolate chips in it to help my soul. It does take up a lot of my daily calories. At lunch I try to have a salad or a small chef salad, again healthy. I try to sneak at least one piece of fruit in as a snack morning and/or afternoon. That takes me down to about 400 calories left in my day. I know that my dinner will cover that and then some so I'll need to get in exercise in order to be in balance. A busy day is too hard to get my exercise in.
Here's the problem. I generally get in a minimum of exercise and I'm in balance - calories in / calories out. But my new problem is on days when I get in longer exercise, I find that after dinner I have 400 calories left and it's an hour before bed time. I don't feel good with food sitting in my stomach when I go to bed so I avoid it, except for maybe popcorn. I cannot plan on mowing the lawn in the evening because my plans get blown too often. For that reason I'm afraid to eat more at lunch and in the afternoon. I will add in a snack before mowing to avoid a low blood sugar but still can't always get the calories in comfortably.
Don't get me wrong, I overeat plenty of days! Leaving calories won't kill me but can I lose weight if I leave them or am I sending my body the wrong signal? I dropped my profile to sedentary because I was gaining weight not losing. Now MFP gives me only 1250 a day.
Last night I finished mowing and had supper at 7. That's the latest I like to eat. One evening I burned 750 calories mowing!