I like your concept! Avoid the boss until you can create the weapon to beat it.
I second some of the other comments here on needing more intuitive controls and communication about how to play the game. A small counter telling me how many items I have left to collect and and indication of when I can attack the boss would make a worlds difference. I also think there's something going on with the 4th boss. I couldn't see how it was attacking.
Regardless, a cute and fun little game!