Scroll View Content partly invisible

So basically as you can see in the screenshot, my Content in the scroll view has its size regulated by two white boxes. The wider, thinner one is the one currently having width 364 and height 15.
I have no idea what the other one is.
Basically it looks like a Rect Transform canvas on its own. Whatever is in the first box but not in this is not visible. Let's say the width of this whole thing is 350, and this box is 300. If I'm instantiating a series of panels of width 350, then the 50-pixel-wide areas on the left are blocked out for all panels.
The problem is I have no idea how to change the size of this box. I have tried changing all sorts of other parameters, but this is not a Viewport problem and nothing on Content's Rect Transform can affect it. I mean I can instantiate 300-pixel-wide stuff instead to make everything stay in this box, but I would really like to change the width of the box to 350.
Thanks for any help!

 

how come the image isn't working...

 

https://imgur.com/WIXdSpb

 

oh right indeed. thanks

 

btw I solved (avoided) this problem by creating a new scroll view and dumping this one... Which means I'll prob stop checking this thread. Would still appreciate any help for anyone having the same question in the future.