That fish is a male and looks like a platy to me. The mouth is the wrong shape for a molly.
I agree. This example pic is def. a male, which would be why the OPs is much rounder in the body if it's a girl. But this fish looks more like a platy to me than a molly. I'm no expert on platies, and I could be totally wrong, but my mollies have a much flatter top-line leading to an upward scooped mouth. I'm not sure if these are differences the OP would have noticed when picking this random pic of the web. If you were simply noticing the coloration, this is a color pattern that could go either way. I think we need a pic of the actual fish in question.