Skin set as slim does not appear as slim in game

I have changed my skin today and set it to be slim as that is how the skin is designed for, however, when I log in it does not appear as a slim skin and instead shows up as the regular steve-style skin with black lines on the arms. Is there something wrong with the specific skin in which I can't get it to be slim? and I have also tried changing my skin again and it will not update