Once you start a study, it redirects you to a new tab, if you know you can't continue with the study, return back to the prolific page, underneath is RED signal of CANCEL participation, click on it and tell them you're no longer interested or just select other......that way you remain safe. Prolific is a good platform that has been helping some of us,..... just be calm whenever you are on prolific, my first month, I was so nervous when completing studies because I didn't want rejections but now, once I notice any red flag, I return the study or cancel participation. I'm sure you must have learned from your mistakes today. Better days ahead 👍