Heading problem on template page

I have created a simple archive page in a child theme for my TwentyEleven based website, but the headings and margins are not conforming to the other pages on the site and I cannot figure out how to change either the css or the php to correct this problem. I’m pretty much a newbie, so please don’t assume I know anything! Here’s the Archives page, and you can click on any other page to see the proper format:

Thank you for any help you can give!