Hello I have created a form on my website. but I would like to make it as wide as the website.

Can I design something like this through JotForm?
Also are you compatible with Wordpress.com?

You can adjust the form width as direct in the article written at https://www.jotform.com/help/35-The-Importance-of-Form-Widths

Yes Similar form on the page  http://www.modmedblog.com/ can be designed using jotform.

Yes, you can integrate the form created, with wordpress by following the instructions provided at : https://www.jotform.com/help/4-Adding-Forms-to-Wordpress-org-Version

Let us know if you have more questions.