How to add a script to the Thank You page?

I want to add a script to the thank you page which is getting displayed after the customer ordered something successfully.

I added my script into
/applications/views/screenportal/tpl/page/checkout_O/thankyou.tpl

because I assumed it would use this template because the page structure was the same in the frontend. I found that out because I made a test order.

However, it doesn’t shows my script. I’ve also added some testclasses to various containers to see if it works, but it just doesn’t work.

I deleted the tmp cache in the shop backend.

Is there another template which displays the thank you page?
Or why are my changes not working?

If you need further information, please let me know.

Thank you.