i havent gotten that far, but im stuck on level 53, can u help ??

help.im stuck on levl 53

im in a room with a telescope and the roof is open, not sure wich level this is, but it has 2 dragon warriors in it, and ive collected all the star signs, but cannot get the last one as my inventry is full, when i try to use them to get the last star sign,nothing happens???

help, im stuck. im in the room to collect all the constaltions, and on the last item which is sagitarious, to pick it up ,i must use an item in my inventry, but when i try, i canot get rid of it to go in the next stage to open the chest! any helpful tips will be welcomed