I Get my Braces off Soon but I Won't Be Able to Get my Retainer Fitted for a Month. Won't my Teeth Start Moving Back?

I've had a top track brace on for over 2 years & a bottom track for over 1 year. I get them off in a couple of weeks & was scheduled to get my retainer the following day. But the other day I got a letter saying the second appointment had to be cancelled so a new appointment was made....over a month later! Will my teeth move a lot during this time?