Was I wrong for putting my puppy down?

I had one of our 4 weeks old pups get hit by a friend and it was yelping and half crushed so I had to put her down with my knife, I have felt like **** ever since it happened, I know the puppy would have died, but everyone was letting her lie there and suffer. I had done some mean things to animals when I was a kid and I regret it all the time, but as I grew up I started taking strays in and giving them good homes and so on, I want to do right with animals but I feel like I am doing something wrong do you think god will forgive me for what I have done in the past and also for this baby puppy?