Thanks for the feedback! Do you think a progress save after each area would be a good solution? I may not have enough code memory left to implement that but I can try.
BTW - tips for the boss: it changes left/right direction when it hits the edge of the screen, it moves up or down at those turns to get closer to the player, and it only shoots when you are far away from it. The trick to defeating is to stick close, fire at it when it swaps direction, then run to the other side of it and repeat. :)