Meh, we all make lots of mistakes with every puppy, child, ferret, kitten or leopard gecko. All we can do is keep on learning and tweaking what we do.
One thing that I keep hearing at the moment and resonates with me is that our dogs’ personalities are a combination of their genetics and their environment. We can never say for sure what “caused” different personality traits in them, so there’s not much point worrying about if we did things wrong when they were puppies. We can choose to change things with the next puppy where we think they could have done better, but you’ll never know if the same puppy would have turned out differently with different environmental exposure.
That’s where I think the skill of reading the dog in front of you comes into play and that only comes with experience.