Hey!
It sounds like you're trying to instantiate an object with Super Text Mesh on it to a UI canvas, and you want the text to be center/right aligned, is that correct?
Please make sure you have "Ui Wrap" checked under the "position" settings. Hopefully that's the cause, it seems to match your description. In v1.7, this checkbox was essentially on by default, but led to some edge cases with how STM worked before I added compatibility with the content size fitter component. So in v1.8, I kept the new feature in as a boolean and had it turned off by default. I guess I should switch that to be on my default instead of off since that would match what most users expect, and wouldn't effect older users.