Footer Ad space problem

Hi

I added a ad space in my footer but it is attached with my blog container margin. I want to match with footer margin. please have a look the image bellow

http://i48.tinypic.com/24q5si1.jpg

I used the code bellow

[mod: please mark any posted code – by following the forum guidelines for posting code – the code below might be partly corrupted]

in footer.php

<div id="footer_ads_720_50">
<a href='http://quicksurvivalkits.com'><img src='http://img9.uploadhouse.com/fileuploads/16343/163437461da0c25cb5fa04151c615a21db8bb677.jpg' /></a>
</div>

in Custom.css

#footer_ads_720_50 {
width:720px;
height:50px;
margin:0px 15px 15px;
}

the ad is attached with blog container. i want to match it with the footer and blog content. also want to up slight from footer copyright info.

Thanks