Q: iMovie

PLEASE HELP ME!

I've edited a video in iMovie on my Ipad (Air 2, iOS 9.2.1). After I finished I looked on the whole video, everything was in place, let's export it to the photo library.

But after I started the exported video, the music of the first scene changed to a random iMovie one. All other parts of the video was all right, just this very first scene (about 4 seconds) changed. I've tried a lot of thing to fix it (changing the music in the whole video, just the first scene, etc.), but nothing worked.

I have to present this video soon at the University and I couldn't do it confidently.

I would very much appreciate your help!! Thank you very much in advance!