Very sorry for your loss - even when it is time it isn't easy.
Your criticism of the way you were treated is valid. Hopefully it will help your vet "clean up" the procedures in his office.
We have had the task of putting down many dogs - the price we pay for the joy we have shared with them. In all but one instance, we were treated with loving concern and consideration. At our regular vet's office, euthanasia is the only procedure that is paid for upfront, if there are two people with the animal. (For us, there always has been - I don't know what the procedure is with only one person.) We are taking to a room, one of us, depending on who has trained and handled the dog, stays with the dog and the other deals with the paperwork, which includes cremation, paw print and paying.
We spend as much time as we want with our pet. When we are ready, the vet comes in. He, sometimes she, no longer explains the procedure to us. They are aware that it's not our first time. It's not a happy time, the vet knows us and the dog and is truly saddened.
After it over, we can spend as much time as we want and then leave without having to deal with the paperwork.
Tom