I already got it on the website but cant get it on steam
The Humble Bundle link you get when you buy it through the website should have a Steam key somewhere on it. Redeem that on Steam.
We’ve changed the widget to itch.io now, @Rainbowglitchy, you should be able to get your Steam key from the download page (press the “Download” button on https://dacap.itch.io/aseprite and then you should be able to see the “Get Steam key” button at the bottom):
If you don’t see this “Get Steam key” button, please contact us at email@example.com
It was helpful