Twentyeleven – Child Theme – Margin Problem

Hey guys!
I have a problem concerning my twentyeleven layout. I made a child theme already. Im using a one column layout and I tried to change margin-right in my child theme style.css. I even tried bigger values, but it does not work.

.one-column #content {
margin-right:50% !important;
width: 100%;
}

I filled the different columns with different colors, so its easier to explain what Im actually doing wrong. Here is a picture of how the website looks like, without changes on margin-right. (Layout)

I want changes in 2 areas:
1) There shouldnt be a margin-top between navbar and content
2) content should fit exactly to the width of the upper layout.

Thanks for help, im trying to figure it out since yesterday. I hope someone is able to help me.