Three months is REALLY young to even begin to expect good come results. I like to play come games at that age, where it is more really of a chase kind of game using the word come as they are chasing after you. It is fun, but they learn the word come means run towards me. Starting off you are right there with the puppy, really enticing them to follow you by playing tug or excitedly offering treats, HIGH VALUE rewards and having a huge party the whole time. "Come" should always be the best thing in the world for your dog because you never know when "come" could be a life saver.
Just for kicks and grins, act like a fool, like you are having the time of your life, get some stinky (yummy) treats and run the other direction, if you notice your dog running after you you can add the word come.
Beware, the word can very easily be ruined to the point where come means something totally different to the dog than what it means to you. One of the easiest commands to ruin. Does come mean run to the fence, go sniff that tree, pick up this toy, stare at the bird, go eat some poop? To some puppies, that is what they think when they hear come because it has been overused during everyday life in which they have not associated any meaning. In these cases it leaves you with having to choose a totally different word to use in place of come.