My voice doesn't suit the songs i like to sing?

when i was in glee club in high school i only get to sing songs that my moderator say "fits" my voice. i always get that i kinda sound like josh groban and should only sing opera-ish or ballad type of songs. but i also really like singing rock, pop and hip hop. i find those type of songs really fun to sing. how can i "train" my voice to sing other type of genre with out sounding weird? it would be really cool if i can be versatile :)