I just saw your note that you're not able to get to a puppy class. If you want your puppy to function confidently in the world as an adult dog, you'll want to put in some extra socializing effort in the absence of a structured class and the watchful eyes of a skilled trainer. At the very least, print off a socialization checklist and start ticking at least a few items off each day, ensuring each experience is short and positive. Always positive.
You'll read all about this in that PDF I shared. Just don't wait to read it! The window for much of this closes as early as 16 weeks.
Some relevant thoughts from Dunbar, as it seems you do have a good-natured pup:
Why Socialize Apparently Friendly and Confident Puppies?
Many breeders, veterinarians and owners simply don’t see the point of early socialization and handling because the puppies are easy to handle and already appear to be confident and friendly. In fact, many young pups appear to be super-mega-confident and overly-friendly and so, why socialize sociable puppies?
Consequently, people are predictably shocked when at about five-and-a-half to eight months of age, their friendly and socialized puppy becomes shy, aloof, wary, standoffish, protective, fearful, reactive and maybe aggressive towards people.
Of course puppies are confident and friendly and easy to handle. They’re puppies! All young pups should be universally outgoing towards people. Fear and aggression do not develop until later in life. Moreover, developing anxieties and fears of the unfamiliar or scary later in life is a normal and adaptive development process.
Adolescent and adult dogs will generally accept species and individuals that they played with as puppies yet they will likely shy away from species and individuals that they did not have adequate opportunity to interact with as puppies. To prevent fear and aggression, the unfamiliar and scary of adolescence must become the familiar and commonplace of puppyhood.
The socialization process is deceptive because all puppies appear to be Mr. or Ms. Sociable at two, three and four months of age and so breeders, veterinarians and owners are unaware that anything is amiss. People are duped by their puppy’s confident and friendly demeanor, not realizing that the effects of insufficient socialization will not become apparent until later in life. But by then of course, it is pretty much too late for quick, easy and effective rehabilitation.