Would it be terrible to say just ditch it and try a different class? Look for something labeled beginner or intermediate. Then it wouldn't be filled with such hard core exercise folks. Try something based on fun rather than strength.

Exercise classes are different, just like people. Find one that works for you, you don't need to feel bad because you tried one that was too much. There's nothing wrong with you, you're trying to take care of yourself, that's great. Just find a class that fits YOU.