Nobody else can do that - If You don't feed us with a full story on what You has done. Mind-reading is very scarce here
• What material did You use - from What Camera etc
• How did You get it into iMoview
• What version of iMovie
• Any other relevant info that can set (at least me) on track.
Yours wanting to help - but there are zillons to be guessed - Bengt W