its all good. the odds of getting deformities is pretty low especially in fish and if you do its a good thing cause then you know that your fish carry a dangerous recessive and you can get fresh stock. With inbreeding it is much more likely that you would end up with inbreeding depression which is the opposite of heterosis (hybrid vigor) In livestock an animal is proven to be a pure breeder by having so many matings with close relatives and no deformities. In people it is highly unlikely that you would have deformities in cases of incest unless it had been going on for generations. That might be more than you wanted to know but i really like genetics.
So enjoy your little platys
