Hey Amy,
The suggestion above should help you widen the width of your input fields. Were you looking to extend the height of your form, or the width?
If your subscribe button is only halfway visible, this might be more of an issue with the element that’s around your form, so not something necessarily within the plugin form’s CSS.
If you’re looking to change the height of your MailChimp form, you can do so by adding a bit of CSS code to your site’s stylesheet:
#mc_signup_form {
height: 1000px;
}
Where 1000 can be any pixel amount you wish.
If you find that the above doesn’t resolve your issue, then it is likely an issue with the CSS that’s around your sign up form. If you’d like, you can post a link to your website and I’d be happy to take a second look.
-tk