Stop worrying...NOW! Lol, just relax and have fun, thats whats its all about. I could just sit for hours, meybe even days, with these birds and its just makes everything slow down and calmer (when you have a generally stressed out personality like mine, man is it a nice break haha). Anyways... my first rule of chicken care is this: Take 99% of what you read, see, and hear as guideline, not a hard and fast rule that must be followed to a T.
BTW, you chick doesn't look sick to me at all, not even a little bit. I mean, unless its got snot running out of its nose or blood coming out of its you-know-where, its pretty difficult to say whether a bird is sick or not based soley on how its standing. So once again, and Im going to steal someones line here, let not your heart be troubled, I'm sure everything is just fine and is going to be just fine! So take a deep breath and enjoy!
One final note, the actual tail feathers are pretty slow to come in, they come in well after the hackle feathers (my 8-10 week old Brahmas haven't got much in the way of tail feathers yet either and they are definately a tailed breed, so meybe yours is a rumpless, or meybe its not. Hey, who knows, suprises happen all the time

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