I'm glad you liked it! Yeah you are right, I need to work on the hitboxes, I'll make them less unforgiving. For the second and fourth level I used a built in filter of Gamemaker on the background, maybe that's causing the problem but I'll have to look more into it, along with fixing some other issues I couldn't solve in time, like the mini boss of the third level, I think he didn't shoot the cannonballs as intended.
Thank you for playing my game!