If you look at the actual nutritional info for half and half, you'll see it has a fair number more carbs than you think:
See Calorie King, for instance
It's just that US food labeling laws allow companies to round up or down rather than give exact numbers. So your 3T should be 2.1 carbs, if you go by what that info I linked to says.
That being said... You know the reasoning behind preferring heavy cream to half and half (higher carb). The higher carb comes from higher dairy sugars (natural) in the fluid. Soooo if you're going to be strict Induction then no, you should find a way to use heavy cream. We're supposed to be getting our sugar intake down as low as it can go while still getting our vegetables. Now, in practice, will that 1g of sugar make that much of a difference? Probably not. Try using the half and half for a while, and if you have trouble losing, maybe dairy sugars affect you. Only way to know is by trying.