How do I open images from safari to the full screen width of my iPad?

You have clearly managed to enable a Safari Slide Over view - this being a major multitasking feature of iPadOS, fully detailed in the iPad User Guide for iPadOS. 

Here is the easy way to change the Slide Over view, to full screen... 

Identify the small grey drag-bar at top-centre of the Slide Over window. Touch-and-drag the drag-bar to the top-centre of the screen - and lift your finger; the Slide Over window will transform into a full screen view.

You may find these overview Apple video guides to be helpful:

After viewing, you’ll be ready for the additional Multitasking Guide:

Use Multitasking on your iPad - Apple Support

The iPad User Guide for iPadOS is also a rich source of information. Here are links to both the downloadable and online versions of the Guide:

‎iPad User Guide on Apple Books

iPad User Guide - Apple Support

I hope this explanation and additional information is helpful in resolving any difficulties you may be having with Multitasking features of your iPad.

Hello cph20surfer,

Thank you for participating in the Apple Support Communities! We understand that images appear on the right side of your iPad screen when opened in Safari. We'd be happy to help take a closer look at this behavior with you.

Is the image opening in Split View like shown in the screenshot here?

Open two items in Split View on iPad - Apple Support

If so, you can either resize the windows or close out of Split View when viewing images in Safari:

Browse the web using Safari on iPad - Apple Support

Let us know if there's no change after trying that step and we'll go from there.

Cheers!