Sidebar and theme issues

Hi all,
I am new to wordpress and fairly new to web design, I’m learning as I go along.

https://gildedpages.net is my site

Yesterday I managed to at least get my site online, and a bonus thing happened: I managed to get shelfari to show up!
Today when I looked at my site, the shelfari graphic is missing from the left side…there is only a text link and a large space gap. However, my husband and friends all see it.
Also, I installed the theme “Retro”, because I liked how it looked and because it said it was fluid width. I took it to mean that I could adjust it so the dark margins on the left and right would be smaller…guess not. I adjusted the width, and it took only part of the background image and extended it to the right. The theme retro looks similar to aged paper, yet when I adjusted the margin, it just widened it with a plain cream color.
I thought “Fluid width” meant you could widen it?
I want my whole screen used, not two thirds of it.
So, I have a question: if Retro cannot be widened, does anyone know if this one can be? It too says “fluid width”…
https://themes.wordpress.net/columns/2-columns/3072/natural-essence-10/

Pardon my ignorance, I am learning as I go. I thank you for your time.
Oh, and my site is far from complete, so if you see an error or an inconsistency, that’s why. I’m working on it, and hope to have it all done within a month.
Also, my husband can translate any tech talk for me, so feel free to use any terms to explain this to my beginners brain.