Hello,
Since your Form File: include/form.php is returning a 500 Internal Server Error which is an indication that this is a Server Configuration issue.
Please consider adding the .customjs Class to the .form-widget DIV and then following code at the very top of your include/form.php File after the opening php tags:
[ch_pre type="php"]error_reporting(E_ALL);[/ch_pre]
which should display all the possible errors. Please notify us about the Error Message you see, after going through the process above, so that we can provide you with more assistance on this. Thanks for your Patience.
Meanwhile, do let us know if we can help you with anything else or if you find any further issues with Canvas.