God was not sorry he made mankind, he was expressing sorrow for what the people had done to themselves.
He was not sorry for what man did, What man did Grieved him. He was sorry he actually made man. That is scripture.
He had to kill everyone and start over, had it not be for Noah, it would have been finished. He rather not have made man, than to do and watch what he had to do. It bothered him that much, so much there is a rainbow in the throne room.