As far as I can see it only comes in this one size - I don't think this is intended to be used as a kind of signature item or badge, but rather as a way to integrate the itch.io store functionality into info pages, project descriptions and the like. You could integrate this into the front page of your project devlog thread, for example - or use it in a game jam thread to present your result in a distinct posting. For signatures and similar, a simple link or image link to the itch.io page are probably more appropriate.
I don't know if there are any customization options, of course, so feel free to discard my comment.
Doesn't matter, thanks for the feedback! Just collecting opinions