September 4 isn’t ingrained in Kelly Clarkson’s brain — but it should be, as its the day she won American Idol. In a video posted Wednesday, September 4, on her Instagram page, digital producer and colleague Andrew Shaw told her, “On this day 22 years ago…” She cut him off, saying, “Oh, my God when you said the date, I got nervous like, ‘Did I miss an anniversary?'” “22 years since winning American Idol,” she said. “You know what? And I’m back on TV. Who would’ve thought? I didn’t even realize what day it was. I’m worried about my kids’ first day of school, which is tomorrow.” Clarkson recen…