When I opened the homepage the E-Mail input field was smaller then the others. The contact form works but I want all fields to look the same.
CF7 now uses the new HTML5 input[type="email"] for the email field in the default CF7 form (installed automatically on every install of the CF7 plugin) and input[type="text"] for the other fields.
Looks like the CSS in your current WordPress theme does not cater for this new HTML5 email input field.
http://contactform7.com/faq/#Why_does_my_email_address_input_field_look_different (recently added to http://contactform7.com/faq/) gives you some guidance on how to make these fields look the same in your current WordPress theme.
See Styling Contact Form for a general explanation of styling CF7 forms using CSS. If you are not familiar with CSS, this page also includes some links to where you can learn CSS.