When I bought new fishes

When I bought new fishes at Pet co, my dad asked for 1 pregnant fish but, the man gave us 4 pregnant fishes. I was so ecstatic because I get to see baby fishes and get more fishes without losing money. I asked the pet co man when the babies will come out and he said at least 2 or 3 weeks but we put the fish in the pregnant box but, the babies are not coming out! 2 weeks already pasted but they are not coming out.