I haven’t yet seen evidence of this - do you have a simple example that reproduces it? I see that image borders are bugged when the image is clickable, but that has nothing to do with cloning.
You set your width to 95%, so of course there’s space on the right - that’s the other 5% of the screen. 
Right here - you have the width of the row set to 95%, which means you’re going to have a stripe on the side next to the row. Oh… are you saying it isn’t filling the 95% wide row? Whats your background picture resize mode set to? Set to cover.
I found some info about cache settings:
In your screen shot, you’re showing it set to contain.
Is the red from the row, or does the container holding that row also have a red background?
I’ll have a look when not on my phone! 
Updated: Yeah, I see it on Thunkable Live/small iPhone. I’m suspicious this is a Thunkable Live-specific layout problem (because the screen height gets encroached on by the header/footer added by Live. So I’m building your project to test that hypothesis. Will report back in an hour or so!
I’m building with these settings:
Ok, not an artifact of viewing in live.
So let’s back up - what do you want it to look like? 95% of screen width, centered, no red?
Sometimes, you just have to do it yourself. This seems to do what you want:
Should you have to resort to calculating it manually? No, but sometimes you just do.