The idea itself is very fitting for the theme! Since it's your first time using Unity, and under such a short deadline, I'd say you done exceedingly well. It works, and it has more than 3 levels :) Some minimalistic midi music would have suited the pew-pew robot sounds. You could even make this into a mobile game with lots of levels, I'm sure people would play it!
P.S. when building your game, go to PlayerSettings in the build window, and look for Resolution and Presentation, to set the game's resolution to a 16:9 ratio. It's not always nice to see the game not filling the whole screen.