Huge blank area

Could you post your site URL here, so I can have a look?

If you want it to remain private, you can also contact us via this contact form:
http://jetpack.me/contact-support/

The margins are created by your theme. Try adding the following CSS code to the bottom of your theme stylesheet, or in your custom CSS editor under Appearance > Edit CSS in your dashboard:

#comments, #respond {
	margin: 0;
}

Let me know if it helps.