Hi Imaran,
First of all Kudos for your 1st Unity Project,
Positives - I can see that you have implemented the concepts that were taught in the class session, its really appreciable. you have aligned the camera properly and used multiple objects.
Improvements could be done are, instead of drawing an alien you could have used some asset store properties which would have made your life easy. You could have used some Background images to make it more colorful.
Good luck with your upcoming projects.