A good first submission
I write this under the assumption this is your first submission.
1: The music, generally, it is a better idea to have a button to turn music down/off, then to just not include it at all.
2: The Multiball, generally it is much better to have all 3 balls be just as meaningful. I believe it is an oversight to loose a life when your primary ball dies, but you still have the other two.
3: What were the enemy missiles doing?
It is a good first submission, and I'm certain it won't take you too long to improve your skills. Best of luck in future submissions.