UGH! poptropica help plez!?

ok, on astro nights island, on the lava planet, how do u get 2 the last rock 2 get on the volcano!? i keep trying 2 jump 2 it but i cant. its too high. and whenever i watch the walkthrus on youtube, the people just jump right 2 it! its not fair, i cant figure out how 2 get up there. could some1 plz help me!?