Header image repeating

Hi
I am having issues getting my header image to display how I want. It repeats horizontally on wider screens, how can I stop this?

Also, the site title displays on two lines on a wide screen, but one line on narrower screens which seems counterintuitive to me! Can I get it to always display on one line?

Thanks in advance!

https://www.janemarshallsilverjewellery.com/

The page I need help with: [log in to see the link]