You can preview your study by navigating to the final studies tab ("publish" tab) when your creating your study and clicking "preview".
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.