No, it's okay! I kind of NEED people to point out where I'm tripping up with this, because I can't always see it - like with the clenched teeth and all! - and 95% of the people who have pointed it out have been very nice and polite about it, and it's fine! Since my face-blindness is only partial, I usually do okay - I've got enough practise coping with it that I can usually work around it - but when I do slip up, I sometimes need someone to go "Hey, did you see what you did here?" so I can fix it.
ETA: And while we're on the subject of same-face syndrome, I want to mention Glen Keane-Face. You know, the way Disney's Rapunzel, Elsa, Anna are practically identical twins if you ignore their hair? It's not Glen Keane's fault, I'm pretty sure - I'm certain he just drew a design, and it was a hit the first time, and Disney just tries to replicate the success over and over and over again, but still - it does stick in the mind. I mean yes, I realise Elsa and Anna are siblings and are supposed to look similar, but seriously?