Home freezers are much colder than those used in ice cream shops. The best way to re-soften your ice cream is to transfer it to the fridge a few hours before serving. You can leave it to soften at room temperature if you prefer, but you'll find that it turns to liquid around the edges, while the middle stays solid.
The only way to ensure accurate measurement of ingredients is with
Metric Kitchen Scales (U.S. option
HERE).