Pumping gas slow to save on fuel?

I always pumped my gas pushing the handle down all the way. My car usually gets around 480km when the handle auto stops. I used to pump a little extra and get 540km but I stopped because I was scared of over pumping once I read about it.

So recently I started pumping my gas extremely slowly. The handle still stopped on its own and I didn’t overfill. For the same price I usually pay, I was getting 635km. Most I’ve ever seen my car read.

The question: is it safe to pump slow and get 635km when I used to push down full force on the hand and get 480km? And is that considered overfilling and is overfilling dangerous to the car?