I did an LFT on Tuesday, and registered it - but hit the wrong box, said I was positive, clicked send, panicked, didn't notice that there was a link to fix it, tried to use the back button, etc.
Long story short, I ended up registering another LFT just so that I could mark myself as non-contagious - but that wasn't enough for the Test and Trace system. The next day I was hounded by text messages, and then called by an operative at the end of the day.
I told them the mistake, and they told me there's nothing their system could do - I needed to call 119 (they didn't tell me which phone system options I needed - It's a horrendous phone system) and get them to mark it as a mistake.
But before I abruptly ended the call with this operative, she told me that until I do this, I'm not allowed out of my house because my phone number was being monitored. I was not polite about the end of that call (I was not rude, mind - not her fault they she has a script to follow - but I was a bit angry)
And once I finaly got bounced around 119 and found the right person to talk to, she said: "Well, self isolation rules end tomorrow - so don't worry about it".
I picked the right time to make this mistake, apparently. But yeah, software has far too much control and extra-legal real-life consequences.