I'd just leave the clean until it's due next time, if it happens again you can decide to bin, or not. Certainly don't stress over it.
Some doors I knock and some I don't.
Sometimes I'll knock to see if the custy is out (then I can get round a bit quicker). But I'll knock and start working straight away, so if they do want a quick chat, i'll work and talk at the same time. I don't mind. You can do it without appearing rude.
Sometimes i'll start without knocking and if the custy comes out and says 'Oh I didn't know you were here', I just say 'Hi, I didn't want to disturb you, a lot of my customers are now working from home'.
It's all good!