I'm using the form to send the user the page title and URL for whicheve

I'm using the form to send the user the page title and URL for whichever page they are on. When the "your email has been sent" message appears is there a way to send them back to the page they were on?

ie. I can't enter a fixed URL because the URL will be different depending on which page they were on.

If I understood you correctly you have link of the same form on multiple pages of your website and you want that your users are redirected back to the page on which they were on before they submitted the form. Unfortunately that is not possible to achieve. When you set redirect link, your users will be redirected to that page regardless of page on which form was opened. 

If you have form on 4 pages of your website, possible workaround would be to clone your form three times and then add different form to each page of your website. This way you will be able to set different redirect page for each of your forms. 

Other way would be to Change "Thank you" URL Based on a Condition. 

It is also possible to create a custom Thank you page with Auto-redirect:

https://www.jotform.com/help/89-Create-a-Custom-Thank-you-page-with-Auto-redirect 

Hope this will help. Let us know if you need further assistance.