You can take the rapid exam online by yourself – you don't need to book any date or anything. Did you get a link to take the exam? If not, it might be good to send an email to email@example.com.
Edit: Rene is right, I didn't take into account the weekend, so you should be getting a link soon.
If you register for the rapid exam, this has to be approved by a mendix academy admin. As it has been weekend past 2 days, you can expect a confirmation today