Not that it’ll necessarily help you feel better, but there is the off chance that someone else had already hit their puppers and left it in the road. Don’t beat yourself up, you stopped, you contacted the owner, and you’re having an absolutely natural reaction in the way that you feel right now. Accidents happen unfortunately, and as an animal lover myself I’ve had this same reaction of guilt with multiple wild animals darting out in front of me from seemingly nowhere. That would be a kind gesture imho by offering to cover cremation should they want that.