That's probably why the veggies are limited to 3 cups per day on induction. 3 cups of veggies won't get you anywhere near 20 grams of carb. It's assumed that you will be "eating liberally" of other foods that while, admittedly, have small amounts of carbs, they do add up. Each egg has about 0.6 grams of carb, salad dressing such as ranch or bleu cheese have 1-2 grams of carb per tablespoon, cheese has 1 gram of carb per ounce and cream roughly 1 gram of carb per tablespoon. Coffee also has carbs (it IS a bean, after all); roughly 1 gram per 8 fluid ounces.
OTOH, if you're not getting close to 20 grams of carb with what you're eating, by all means feel free to have some more veggies.