To know whether or not your opt-in page is converting, you will need to drive a certain amount of traffic to your page.
As a general guideline, you want at least 200-300 unique clicks to your opt-in page. This will give you a healthy sample size.
Furthermore, when driving cold Facebook ads to your opt-in page, you are looking for a conversion greater than 20% minimum (ideally more).
Often students feel their opt-in page is not converting after only driving 20 clicks, there needs to be more!