Logging gym classes (cals burned)

Ok, I gotta ask - MFP shows I burned 980 cals in one hour of Zumba. As much as I know how much I sweat, and I put in a huge effort, it's hard to imagine I really burned that much.... so I manually changed it to 580. I'm not planning on eating back my cals tonight anyways. Curious on whether or not I should change it or leave it.

--> I'm assuming the cals MFP calculated are based off my height & weight. Is that part accurate?