Yes, you can have 3 platys! Platys are a type of freshwater fish that thrive in small groups. They are social creatures and prefer to live in schools of at least 6-8 individuals so having three is okay but more would be better. A larger school will help with the stress levels of each individual fish and also provide them with more opportunities for play, exploration, and interaction. When keeping multiple platies together it's important to make sure their aquarium is large enough to accommodate all its inhabitants comfortably as overcrowding can cause illness or aggression towards other tank mates. You should also provide plenty of hiding spaces as this will give them somewhere secure to retreat when feeling threatened or stressed out by other members of the group. Overall, if you're looking for an inexpensive way to add some color and life into your home aquarium then three platys might just be the perfect choice!