You can preview your study by navigating to the bottom of the study creation form and clicking "Preview".
This option allows you to test your study exactly as it will appear to participants.
If you are redirecting participants to a Completion URL at the end of your study, and this is working correctly, then you should receive a message like this when finishing your preview:
Note: "TEMPLATE" will be replaced with your study's completion code.
Sign up for a participant account (with an email that is different from your researcher email), only make the study available for yourself via the Whitelist feature, and then take part in your own study.
By signing up as a participant, you will be able to see everything that participants can see when they register on Prolific (incl. which prescreening questions we ask them, etc.).
Then, from your participant point of view, you can start the study and simply return the submission, so you don't have to pay for it. You will notice that in the review section in the researcher dashboard, your participant submission will be labelled as "Returned".
You can duplicate this study and run it again with your intended sample size.
Please note, however, that you will need to verify your participant email address and phone number before you can access your study. More information about verification can be found in our Participant Help Centre: https://participant-help.prolific.co.