If you are clumsy and stubborn, you can hurt yourself trying to keep up in a class, no matter what it is about. Try not too be too stubborn: Arrange a signal with your body that means "stop". (I'm speaking from experience here.)

Usually, free weights are pretty safe if you pay attention to them, and to form. Don't let the speed and rhythm of a class tempt you to pay less attention.

Start out light. What I've seen from a (maybe) similar class in the gym that I go to, they are doing enough reps that it would be exhausting doing those with a pencil. You can always go up.

Also, what rydra_wong says about low weights and endless reps. But I still think that a class, carefully taken, might give you some familiarity with free weights that can only be useful.