Are you supposed to be meeting the driver? All of my DoorDash deliveries are no contact only. They leave them and send me a text that it's been dropped off. Perhaps that is what your driver expected, and didn't expect to see anyone.
Why did you throw the food away? It should be all sealed and wrapped. The dasher doesn't prepare the food, just picks it up.
Listen, I get the fear. I'm higher risk, live in one of the states with the most cases. I get it. But I think it's also important to not panic needlessly.
This isn't in response to the risk, which is slight because the contact was very short and not intimate. I'm not sure why you threw out the food, there was no connection between that and the delivery person. But I would want to know if the person expected you to come outside and greet her. A lot of deliveries are being left on doorsteps or other places. But if this was an expected contact, I would no matter whether you get tested or not call Doordash and let them know, as all the delivery people are supposed to be masked if personal contact is expected. Otherwise, I agree with the above, I'm just more concerned this delivery person gets her act together.
I'd say you are not at risk. Take a test if you are anxious but it really doesn't sound like you were exposed to the virus.