Wolf not only did you not anything wrong, you did exactly what should be done in such a situation. Kol yisroel areivim zeh li’zeh, both in gashmiyus and ruchniyus. If I’m not mistaken, the Mishna Brura actually says that one should yell at people talking during davening, but I always took that to be the last step (ie stop them from talking even if you have to yell at them) and that doing it nicely is far better.
Actually, I had a pretty similar situation myself this morning; during shachris, two people in front of me kept shmozzing. My first step was (as it usually is) to daven extra loudly while looking straight at the people. This time that strategy didn’t work, so in between paragraphs I gave a low “shh”. Sure enough, a couple of seconds later they stopped talking.