I wonder how (or if) he will respond.
Given we have much more serious issues to deal with (and I am not saying breaking the covid law is nothing, just that the war with Russia is much, much more serious), I'd say just pay the fine, apologise about the apparent misinterpretation of the law (to the nation and the queen) and move on.
My concerns about Boris of this sort are the ones that concerned me beforehand and that I had to swallow when he became PM because he also had more positives to offer than the other candidates. He's done fairly well on the major things that matter to me. And here we have the negatives, too.
Silver lining. I am also pleased that a PM can be found to have broken the law. That's the rule of law in action.