Personally I always aimed for as close to 20 carbs per day as possible. I think (I might be wrong,. but this is the way I do it) that the 3 cups of vegies should be taken as a 'minumum' requirement, rather than a total requirement.

More vegies is always a good thing IMO It also might help you lose faster, I noticed in another thread you said it was quite slow going for you??