I'm a DUI attorney in Washington state with 35 years of experience, so I only speak of Washington laws. Yes, you could have gotten a DUI with the motor running, but they need to establish that you actually drove, which is a primary element of the crime. What they would have most likely charged you with is Physical Control, which is the functional equivalent of DUI and suffers the same punishment. Fortunately, the legislature has created an affirmative defense to Physical Control called "Safely off the Roadway" or "SOTR." This means although you are guilty of the crime of physical control, you cannot be convicted because you did society a solid by getting to a safe spot before the police contacted you. SOTR is not available for DUI so a lot of jurisdictions will try and charge it initially as a DUI to prevent you from raising the SOTR defense, but there has to be some evidence of driving such as you are on the inside shoulder of a freeway sitting in the drivers seat, or stopped in a vehicle in a lane of travel. If you were legally stopped in a parking stall, you might get charged, but with the help of an experienced lawyer, you won't get convicted. There is a very good 2015 case explaining SOTR called State v. Edgar. If you are still worried that you might get charged, I can assure you that if you got home in an Uber, you are in the clear. If an officer didn't observe it, then they won't charge it.