I've never hatched chicks from my own incubator before, but what I have learned from other people's posts is, when hatching, you're always learning from your mistakes. I'm sure it'll happen again because there is no such thing as a perfect hatch. Don't feel bad, it happens.
I'm sorry to hear about your little chickie ... but thanks for posting the pic. My kids are learning about chick development as we go and this is a good photo for them.