Increase Width Of The TwentyTen Content Area

Ive increased the width of the wrapper in my TwentyTen child theme from 940px to 1200px and would like to increase the content area to the same as the wrapper, 1200px.I’m using a one column, no sidebar template. I’m planning on placing a series of images that covers the wrapper area from left to right with no spaces (six images each 200px wide). This seems to work fine when i set the wrapper at 940px and the content to 940px.
When i increase the wrapper size to 1200px and the content to 1200px the wrapper increases but the content stays centred and displats only 940px cropping out 260px of content.
Here is the css code ive altered
`#wrapper {
margin: 0 auto;
width: 1200px;
}
.one-column #content {
margin: 0 auto;
width: 1200px;`
Thanks