Hi,
I can reproduce your issue in the client of Outlook.
However, when the same email is opened in the web version of outlook, it appears to be centered.

So I did some search about it and found this post:
Valign not working in Outlook HTML Emails - Stack Overflow
I tried to modify the “line-height” in the text style from the HTML of the email.
This does work for Outlook, but at the same time other email clients will become uncentered.
This should be an issue with Outlook's support for HTML email formatting. Similarly, there are issues such as multiple columns in a row not being displayed side by side. So it is recommended to seek help from Outlook's forum.
If this helped you, I'd appreciate it if you'd mark this as a Verified Answer, which may in turn help others as well.
Best Regards,
Nya