How to Scale an Image in UMG to the ViewPort Size?

I want my umg image to resize via the resolution of the viewport, currently it just shows the image the size set in umg 1920x1080, and if you have a smaller resolution it just shows the center of the image not the whole image resized.

I’m trying to make an after image for a flashbang effect and it works great in 1080p, but if I change the viewport size(resolution) then the after image looks bigger than what I’m seeing and this just won’t do!

I got some pics to show what I mean/what I’ve got.
resized viewport, He’s HUGE!

working good at 1080p (the set image size)

wrapped it in a scalebox but that didn’t work