Man, come on, you really think hitting no made you a jerk? That lady behind you was the rude one (30 seconds is nothing, people scroll their phones for way longer than that at checkout). The round up thing is a trap anyway, stores use your four bucks to look good and then take the tax write off for themselves. You gotta remember Kroger is a billion dollar company, they don't need your four dollars, and half those round up programs don't even send the money where you think. Your rule of picking out your own cans is way better because you actually know what you're giving and who gets it. So no, you did nothing wrong, the only mistake was letting some stranger rush you into a choice you weren't ready to make.

47 in a month? That seems low honestly, I feel like I hit that in my first week alone. The same three mistakes thing is so real though, mine were forgetting colons, messing up indents, and spelling print wrong somehow. Once those clicked the errors dropped off a cliff and I finally felt like I wasn't totally hopeless.