How do I?

[Gralion]

How do I get off the Rainbow islands I havnt got all the badges or beaten the elite 4 and I cant get out How do I do it?

[Don't Run With Scizors]

I had problems with this for a while myself. You'll have to rescue the little girl in the forest from the Hypno, first, then you'll have to go and talk to her parents and receive some item (not sure what is it). Afterwards, go back to the Pokémon Center on the first island, and after a little dialogue with the man who took you to the islands in the first place, he'll take you back.

[Carbonite4]

I don't have the games, but can you go to and from the islands whenever you want?

[Don't Run With Scizors]

Yeah, you can get to it from the port in Vermillion City once you've returned from the islands to Cinnabar the first time, I think.