Lecture Hall Cop

So the professor is ending the lecture, but there's still time left and he's still giving out information.  He's not just chatting or anything.  There are ~100 students in the class and once they figure class is wrapping up, a whole lot of students rumble around packing up and talk amongst themselves.  I look back (I'm the TA), and see one of my students in particular joking loudly to the person next to him.  Grrr... Overread gets ticked.  The professor has been having a hard time holding their interest throughout the class anyway, but we're not even halfway through the term, and I'm afraid it's only going to get worse.

So.  After class is over, I go over to the students that I saw talking and tell them that they need to be quiet while the professor is speaking.  They protested their innocence.  I was probably a bit forceful, but I don't think I was particularly nasty.  I made it clear that they were disrupting the class, and this was unacceptable. 

I know this seems minor, but it was a pretty big thing for me.  I really don't like doing that sort of thing, especially with a big audience (all of their classmates were around).

Maybe I'm just too paranoid, but I'm wondering:

• Did I see it wrong?  Were they the ones that were talking? (I'm 99% sure they were, but the 1% is killing me)
• Am I placing my frustrations with the way the class is being taught on the students? (The professor doesn't have the most powerful stage presence, and many students were rumbling and chatting.  Both of these things frustrate me.)
• Do I need to make an announcement in my sections (Yes, I do.  But what exactly will I say?)