Hi texasma,
That's a bummer! I'd agree with Laststraw because it's better to err on the safe side. Or keep the amount you are used to, after all it's something you love, and see if you can trim something else from your day's menu. Before you do that, here is a suggestion:
Either your scale is out of whack or the nutrition info on the carton is inaccurate. Even melted sherbet shouldn't increase by that much volume.
I'd check the basics...making sure your scale is on a hard flat surface, batteries are fresh (if it uses them), and calibrating it, if applicable.
Also try weighing some other items to see how it compares to their package-stated weight. 84 grams is about 3 oz, so you could, for instance, weigh 3 pieces of individually wrapped string cheese (1oz/each, & unwrapped) Or something similar that you have on hand.
Also consider calling the company--if your scale is accurate, there is a discrepancy. Hope this helps