CC clothing glitch

I only learned about CC recently and today I decided to try making my own. I added an image to an existing shirt in the game and changed very little. I exported it as a .package file and added it to the game's mods folder. When I view the item in the create/edit a sim menu it appears normal but when I try to use it the sim appears with the mesh of their clothes but all the clothes are transparent and they appear naked. I'd love if anyone can tell me how to fix this. Thanks