Hi Matt,
I checked your site, and you're using Header ID name, with Menu ID name. And this should help:
#sp-menu>.sp-column.justify-content-end {
justify-content: center !important;}
Tip from Helix documenation >> https://www.joomshaper.com/documentation/helix-framework/customization-tips#how-to-change-the-position-of-the-menu
Remember to add it as first line in Custom CSS just in case you may have issues in syntax below.
BTW
If you talk about Header, do not use expression/phrase "top bar" becuase in most cases it's different row(!) in the gird. Is a small detail for you, but for Us important detail.