If just sitting still caused DVTs, everyone would be dead soon, pregnant or not.
That said, is it "absolutely impossible" to get a DVT as you described? No--just extremely unlikely. DVTs are UNCOMFORTABLE--that is what prompts Dr visit. Do you have a new pain in your leg? Is it hot compared to other one? Swollen (or more so) compared to other one? If no to these, then I would not worry.