Go theme – large margins

Hi all, I am super desperate for help.
I am using the Go theme on my website.
I programmed a gallery-type script which cycles through youtube embeds using iframe as well as images.
Everything works according to plan when I run the script through my browser, but after using shortcode to display it on a page instead, all of my videos and images seemed to be squished into a very skinny container. Manipulating the margins in CSS allowed me to shift things around a bit, but not in the way that I wanted to.
If there is any way to change this or any tag that I have not yet tried, help would be greatly appreciated! Here is the styling I used:

.center
{
display: block;
margin-left: auto;
margin-right: auto;
width: 90%;
height: auto;
}
And the extra styling for the iframe:
.iframe-container
{
overflow: hidden;
padding-top: 56.25%;
position: relative;
}

.iframe-container iframe
{
border: 0;
height: 100%;
left: 0;
position: absolute;
top: 0;
width: 100%;
}`