If you are going for a difficult game try to make it more fair, I mean the final boos 3 shots me and I have no invincibility frames after I get hit, the power of healing after 10 seconds is useless if you die in only 2 seconds. And also I would suggest to make your own assets for your next project even if you don't have experience.
I hope that you will keep up doing games even if you didn't quite hit the target this time, but hey that is how you get experience.
Keep it up man!