I'm so sorry for your loss. It was a really adorable chick.
Sometimes they're just not strong enough to make it for whatever reason, and no matter what we do they pass away. It's just a part of life, but of course that doesn't mean we shouldn't be sad about it. Try not to blame yourself--it sounds like you were doing all you could for the little chick!
My daughter and I had gone to TSC about a week ago to get supplies and moon over the babies. They had a shipment of the banty chicks. I don't know how they are strong enough to survive and sure enough they had a little one dying in the brooder. My daughter and I took turns trying to revive it and at least comfort it in some manner so it didn't die alone.