Why does my form take up a lot of white space at the bottom of it?

There is a huge white gap below my form in my Wordpress.com site. How do I get rid of it and make the box smaller?

There's no white space in the stand alone version of your form, which makes me think it's a styling conflict with your website, to avoid this, please try embedding your form using the iFrame method. 

Please refer to the following links for more information:

Getting the form iFrame code

Adding a Form to a Web Page

Thank you.