How is the little one doing? I sure hope he/she makes it. Sounds like you are doing ok. If it is a preemie, it will take time to "catch up" so I am glad you are working with it and giving it time, rather than just culling it. What a cutie.
Sometimes things are just not meant to be. I tried saving 5 different chicks with my last all, and all 5 still died, although one lasted longer than the others. The yolk sac may have gotten infected before absorbtion, or because he was a premmie, he may just not have developed enough to survive. You did everything you could and made his days on this earth happy and comfortable. You are a good person