Parenting ramblings

Why is it that I can do 100 things right for and with my daughter, but if I'm stressed and short with her, I obsess about it til no end as if it's the end of the world?
We went shopping at Walmart tonight, to get some groceries before the storm and to get tires put on the truck. The tire thing was a flop. The tires we want put on are one size too small and they won't do it, but the mechanic told us to go to a "real" repair shop and they would do it and he was nice enough to recommend a place to do it. On with the shopping trip.... After being separated several times, we finally got into the food aisles where we attempted to get food. Now, I'll admit that I was not as prepared as I usually am. I hadn't wanted to go food shopping until the kiddo was back in school and I could go alone, but I realized that the storm they are predicting may keep us in the house for a day or two and our cabinets were looking a tad bare and probably wouldn't have held us over. I knew I should have ran to the local store and left the kiddo with Daddy but frugal me knew I'd spend too much there and I could get double the amount of stuff at Walmart. Kiddo was not such a great camper in the store. If she wasn't asking for a hundred different things, she was complaining about a hundred different other things and if those two weren't in effect, she was employing some other annoying tactic. I stopped mid shopping and explained to her that her actions weren't going to yield great consequences. I told her what those consequences were going to be, she was warned. By the end of the trip, she was in tears, I was tired and Daddy was just ready to call it a day and go home. I spent WAY more than I should have, I have no idea what we bought but I know it's definitely not going to make decent, healthy dinners and healthy lunches. When we finally got home, I made the kiddo oatmeal and made her get ready for bed. But I was short, annoyed and exhausted. I wasn't as nice as I could possibly be, though heaven help me, I tried but she kept "needing this" or "having to do that" and I just wanted the night to end. I'll obsess over not giving her a "perfect" bedtime. Nevermind that the night before she went to bed peacefully, my heart spilling with love or that she will have a perfect bedtime tomorrow night. I'll obsess about tonight, the night that didn't go well.
And as I end this, she has just come out of her room asking to go to the bathroom, even though she was in bed an hour ago. I'm just tired, it's been a long few days, we're all sick and I just need to rest. In the grand scheme of things, she won't remember this, she'll remember something else but it bothers me, right now.