There is no fix. This is the way that Flash works. If you put things in the timeline they will play back. How well or poorly they play will depend on what you have designed and how capable the computer is at reproducing what you've designed. Flash plays back from the .swf at runtime using the Flash player. This is different from the way that digital video plays, for instance.
If you place a sound file instance in the timeline by attaching it to a keyframe, that sound will begin to play as soon as the playback head hits that keyframe. The sound will continue to play until it has finished. If you want to have more precise control over the playback of the sound, you'll have to use Actionscript. Here is a good tutorial on the basics of sound control with Actionscript: http://www.schoolofflash.com/2008/03/tutorial-using-sound-in-actionscript-3/.
Adobe also has some very good introductory videos on Flash. You may want to go through some of these to get more familiar with the ways that you can work with Flash: http://tv.adobe.com/watch/flash-in-a-flash/episode-1/