can't tell without looking at the actual problem. If you did it in the unpublished theme, you can get a link to it by right-clicking the eye button and copying link address; then post it here (similar to ....myshopify.com/?preview_theme_id=164953477).
You've most probably lost an <a> tag somewhere.
I know this post is from 2017... I've been trying to do the same on my site for few days: www.bonvoyage101.com, to centre the logo in the header.
I have very limited skills in HTML unfortunately - when I tried the best I could do was this (see screenshot below), the logo moved a bit to the right, but my actual logo disappeared and has been replaced by just text.
If anyone would be able to help I'd be really thankful.
I believe my solution above still applies, but if you need help implementing it -- my e-mail is right below: