Lets hope this is your only mulligan
If you want to make the filesize CONSIDERABLEY smaller, convert the mp3 file to wave.
An mp3 is basically an already compressed file. So flash doesn't compress it very well. Wave files are uncompressed which allows flash to compress it 50 times smaller than its original size.
All you did was make a few movie clips and have them fly around the screen. Not very difficult. Keep trying.