Thank you for helping! 
I did disable the layer mask and by doing so I was seeing the fully opaque sticker.
Dumb Question/Annotation: When I export the image with a deactivated layer mask the information of the layer mask is not transferred with it, right?
To give one more input, please take a look at how stickers scrape in CSGO:
In the video the stickers are fully opaque. When you scrape them, they were off in a certain way according to the information in the alpha channel.
I edited the alpha channel values to my liking but the image (the sticker) logically becomes transparent and when I export the sticker, it stays that way (transparent).
I did disable the layer mask and by doing so I was seeing the fully opaque sticker.
Dumb Question/Annotation: When I export the image with a deactivated layer mask the information of the layer mask is not transferred with it, right?
To give one more input, please take a look at how stickers scrape in CSGO:
In the video the stickers are fully opaque. When you scrape them, they were off in a certain way according to the information in the alpha channel.
I edited the alpha channel values to my liking but the image (the sticker) logically becomes transparent and when I export the sticker, it stays that way (transparent).