Here are a few things that you can check to make sure that video and audio always remain synchronized:

1) The start time of both video and audio clips should be the same. To know the start time select the video clip and view its start time in the Time box present to the left of the timeline scroll bar. Now, select the Audio Clip and check its Start time.
2) There shouldn't be huge variations between the frame rates of videos you add to the timeline and the frame rate you select when you make your movie. If you are not sure then select a frame rate between 15 - 30FPS. The Files List in the Collection window displays the frame rates of all video files.

It is recommended that you always save your project before making your movies so that you can edit them later. If you haven't saved your project then you can try opening the movie with Video Edit Magic again and adjusting its video and audio part.