I see Paul just mentioned you were in a high risk area, that does change things.
If I did have to set them down I would take them to the farthest place possible. For instance when I took Delgado to Petsmart (in my arms of course) it was in a strip mall with a HUGE parking lot, I literally walked to the opposite end of the parking lot from Petsmart and let him pee there before taking him inside.
I tried to stick mainly to places where there were tons of humans but limited dog areas. At two shots they've got a decent immunity but I don't trust it 100% until 1 week after the 3rd shot. I've personally never had to deal with parvo and I hope I never ever have to, it's a scary disease