I'm having my braces off on wednesday but not having my retainer till a week later; will my teeth move?

Should be fine. Even if the teeth move minimally, the retainer will nudge them back into place.. Express your concerns to your orthodontist.
Not noticeably. Even if there is minimal movement the retainers are made to the position your teeth were in at braces removal, and will nudge your teeth back into place. Be sure to wear them exactly as directed. Go looking for reasons to put them on, not excuses to take them off.
Minimally so. Nothing the retainer won't correct. Make sure you wear your retainer as instructed. Hope this helps.