This is due to CSS styling applied to standard HTML form elements within your current WordPress theme.
To change the style of your CF7 forms you would need to edit the CSS style sheets used by your WordPress theme.
See Styling Contact Form for a general explanation of styling CF7 forms using CSS.
There is a link at the bottom of the page to a comprehensive and detailed article on Styling Contact Form 7 Forms.
??I use Ordered List elements to display multiple fields on single line.
HTML:
<ol class="singleline">
<li> <label for="your-name">Your Name (required) </label> [text* your-name] </li>
<li> <label for="your-email">Your Email (required) </label> [email* your-email] </li>
</ol>
Added to Form section of CF7 interface. <label> tags are added for improved accessability.
CSS:
.wpcf7-form .singleline ol {
list-style: none;
margin: 0;
}
.wpcf7-form .singleline li{
display: inline-block;
margin-right: 10px;
}