PotC:At World's End help

Hi all, trying to finish this game off and im stuck, i need to get the jackanism chest from lvl 1 (Prison Fortress) and lvl 6 (Isla Cruces) i know where the chests are (right at the start of the level iirc) but i dnt have any shrunken heads, ive heard u can replay a level and get 3 heads then save and restart the level required... yet when i try this i cant save. Someone please help, would love to get this game finished :)