It looks awful on mobile devices.
Could you provide a screenshot so I can take a look? Pictorico is designed to look good at any screen size, so it would be helpful to know what you’re seeing, since it looks good from my end.
Here’s a guide on how to make a screenshot:
https://en.support.wordpress.com/make-a-screenshot/
You can upload the screenshot – in a graphic format like JPG, PNG, or PDF – in your Media Library, and provide a link so I can see it, or upload it with a service like Imgur or Snaggy.
Also I have a custom header image and it gets clipped on small mobile screens. How can I prevent that?
The header in Pictorico may be cropped on smaller devices to fit the screen size.
You might like to try experimenting with media queries in your custom CSS to change the display on different sizes of screens. Here are some good resources to get you started:
https://en.support.wordpress.com/custom-design/custom-css-media-queries/
https://css-tricks.com/snippets/css/media-queries-for-standard-devices/
https://webdesignerwall.com/tutorials/responsive-design-with-css3-media-queries
Media queries are a simple concept but powerful in practice, and can take some experimentation and testing to get right. Good luck!