This question came up in a discussion group recently. A member was told "over socializing" had led to her dog thinking they could go see whatever dog, human, or thing they wanted anytime. And another was told it had caused her dog's "dog aggression". (Side note, if a trainer shames and blames you, don't go back.)
An impulsive, environmentally focused dog IS a problem, if you ask me. And a reactive dog is a problem if you ask almost anyone. But rather than self blaming, finger pointing, and suspecting the incorrect causations, let's break this down.
Socialization is habituation to the environment through exposure. Overwhelming stressful exposure is harmful. Lots of good exposure is not.
You definitely need to be attuned to your own dog and cultivate experiences where your pup feels safe. Make sure they are enjoying their new, big world. For small dogs consider using a sling so they feel your warmth and comfort. Support your dog in NOT engaging with people or dogs if they don't want to. I held my own puppy the entire first week of Puppy Class. If your dog doesn't want strangers to pet/hold them, consider having them drop a treat instead. Or just hang out and let them watch.
Only allow dog socialization with carefully selected dogs.
Rambunctious players may overwhelm your pup causing stress and social behavior problems. If you have a breed that tends to be dog aggressive work with an experienced trainer on cultivating their dog socialization. If not, take it slow with dogs and focus most of your time and energy on cultivating good experiences with diverse people and places.
As far as "too much" socialization. Your puppy needs a lot of rest so you don't want to exhaust and burn them out. But continuous social exposure to sensory stimuli will, if anything, lead to habituation and satiation. In other words people/places become old news and less interesting to your dog so they focus on you more. In and of itself, it doesn't drive impulsivity.
If your dog lacks impulse control and wants to run and greet every dog and human they see, and becomes frustrated and acts out if they can't, this is a training issue, not a socialization issue.
First of all, there is no need to self blame or feel guilty about anything you did with good intent for your dog. There has never been a perfect human in the history of the world. And dogs and humans have evolved together just fine.
Secondly, socialization only maximizes the social genetics your dog was born with. So you didn't "make" your dog anything. You developed what is actually a gift they were born with. You might have unintentionally rewarded bad behavior. But that's OK. We can change that.
What probably HAS happened is your dog has learned that pulling, jumping, and barking has led to getting what they want: Play, butt sniffs, "saying hi", and attention from other dogs and humans. Remember the laws of learning are like the laws of gravity. Always in effect. And, depending on their breed, some of them have really low frustration thresholds. So they will act out quickly if they see something they want and don't get it.
If you are in this boat, you need to make changes before your dog develops more barrier frustration and drives you crazy. But don't worry too much. Your dog can develop impulse control and handler focus. Start by making a list of the things they want. And start controlling their access so they get what they want for doing what YOU want. A professional trainer can help you with this. And they can help you understand how your dogs breed and age are playing into this behavior and what realistic timeframes and results look like.
What if my dog has a bad experience during their socialization period?
Don't stress. If one bad experience was going to cause long term problems it was going to happen one way or the other. Just spend lots of time training and doing fun things with your pup. Then go back and try the experience again with some intention and control. For example the first time I took my child's service dog in training to the grocery store I had not appreciated how loud the carts are, let alone to a puppy's sensitive ears. We got through it. Did lots of other enriching things and then tried again with some plans to mute the noise.