How much heavy cream should I use in the filling. The Cups and grams measurement don't seem to math

Not sure where that weight came from - but you are correct. I don't ordinarily weigh liquid ingredients either- I measure them in ml or liters, if I'm not using American cup measures. If you do that, then you need roughly 79ml of heavy cream. That's the measure I'd go with, instead of worrying about the weight part. Maybe Erin will have more insight to offer, and clear things up. In the meantime, I'd go with the ml measurement though.