If you really want to get into class you'll be here all week, there've been lots of threads before about what constitutes different classes, I'd suggest looking at those. Essentially we have a lot of historical and cultural baggage, so it's never as simple as how much you earn. As an American you're largely exempt from those judgements, take advantage of that!
The comments aren't really negative, just making sure you know. Some upper middle class / posh names can sound a little pretentious but you'd probably get away with it. As an American living here (and college educated) you'd be assumed to be middle class in our terms.
Can of worms as it is and against my own advice, I am happy to procrastinate for a moment more. I'm 38 so apologies for the age of the references:
Upper class is essentially aristocracy so no direct comparison but the families at the top of your political system, or descendants of the first pilgrims may be similar.
Frasier and Niles Crane and their associates are upper middle class. Martin Crane is working class, married into middle class. Daphne's family are working class.
All the Friends characters are middle, middle class, though Joey's background is working class and Rachel's family may be upper middle (or rich lower middle depending what her parents do and are like, can't remember).
Roseanne Barr's character in the Roseanne sitcom is classic working class.