Glad you’ve chosen to go with GeneratePress!
This is actually more complicated than it should be, but it is possible.
You can try out this plugin: https://wordpress.org/plugins/html-in-widget-titles/
Then, you would replace
> in your HTML with
So, to center:
[span style="text-align:center;display:block;"]My centered title[/span]
That should work.
Let me know 🙂