Okay had a look at your site… I found that your theme is using the following bit of CSS for “input” and “textarea” fields:
input, textarea {
width: 94%;
padding: 8px;
font-family: Arial, Verdana, sans-serif;
font-size: 1.2em;
border: 1px solid #ccc;
}
You can see that it’s forcing every field to be 94% of the container width. I am not sure why the theme is specifying every input fields to be of a certain width (it only limits the capability of your theme). If you get ride of that line it should fix your issue.