1. Get Three Column Form With Full Submit Button as in Title Box Shortcode

In case you are creating fresh form, fields may stack up, instead of appearing inline, even the checkbox made available in Title Box shortcode is checked.
It may need minor tweak, in forms’ edit screen.

Just follow this:

• Wrap complete form code in a div ‘submit-full clearfix’
• Wrap each input field and submit button ( HTML / Shortcode ) in separate ‘p’ tags.

So form code on its edit screen will look something like this:

If it is HTML:
<div class="submit-full clearfix">
<p><input type="text" name="NAME" placeholder="Your name" required /></p>
<p><input type="email" name="EMAIL" placeholder="Your email" required /></p>
<p><button type="submit" class="dtr-form-btn">Subscribe</button></p>
</div>

If form fields are available as shortcode:
<div class="submit-full clearfix">
<p><[text* your-name]</p>
<p><[email* your-email]</p>
<p><[submit "Send"]</p>
</div>