Ugh, I think I'm going on 35 tries now, I lost count. I want my $65 back

Finally got past chapter 6 boss, got through chapter 7 just now as well. Not sure I want to put myself in a position to be frustrated any further though, I might just trade in the game and move on.
End of chapter 9 boss, another shitty boss battle. I get the damn worm down to 1/3 of it's life and it does some kind of attack that drains me all the way and kills me. Urg...