Adjusting Section Background Image to match Mobile

I need help making my Mobile Section Background exactly the same as it's viewing on my website view. It's blown up very big and I'm not sure how to fix it.

Can you share your website URL?

 https://moonmashkiki.squarespace.com/home

Also now I'm having an issue with the main website looking too blown up as well so any recommendations to pull this all together would be great

The background image being blown up on mobile is because the background image needs to cover the background, so the top of the image is at the top of the section and the bottom of the image is at the bottom of the section, on mobile you have a long scrolling experience and the only way that the image can fit behind all of the content is to be very tall and crop in at the sides. This is inherent with using a background image, but careful consideration when you pick the image as well as thinking about how long the section is on mobile can improve how the image looks. I generally recommend a background image that is 3:2 ratio, but in your case you might want a portrait image.

This is a visualisation of how your background image will be cropped on desktop and mobile, and why the background seems so zoomed in on mobile: