Oh, Ginger, you did everything you could for your little Boudin Boo!
You gave him his last moments with you, in the park on a soft blanket, out in the open air with the blue sky above, and you didn't know his little heart would stop right then and there in the car. I know you said that you feel blessed that you didn't have to go back to the needle, and of course it's so easy to second guess ourselves with "what if" or "may I should have" or "why didn't I". For some, the gentle passing with the needle is our only choice whether at home or at the vet, for others, a peaceful passing during sleep is a blessing, and for others, being with your beloved baby during the last moments is what a Guardian Mom or Dad wants to do, no matter where this occurs. I don't think there is a right or wrong about our choices or the options we have. We do what we think is best at the time, because we love our babies so much! I am so sorry for your loss!!!!
Heaven is the place where all the dogs you've ever loved come to greet you.