Braces are coming off, but no retainer. What could happen?

It's finally prom/graduation season and my braces are coming off after a whopping (seemingly forever) three years! My scheduled appointment to remove the braces is this upcoming Tuesday. However, I never received the mold to create the retainer. When I asked my orthodontist why, he replied, "I want them to settle first, so we'll wait a bit" or something to that matter. Thing is, prom (and graduation) is the week after and the whole point of braces is for them not to settle! I don't know if he is waiting a week or something, but I'm worried. This guy has given me so many problems in the past and now that they're coming off, I feel like this is just another. What's the worst that could happen?