This is more of a problem with the map generator. If you load up the Editor & select a Huge World on Archipelago Islands... you don't get islands. You get jagged continents with a few islands. Even in the game if you view the picture for Archipelago with 60% water & Continents with 70% water they look almost identical! I wish there was a better variation.
To increase your odds of getting your own island - increase the water to 80% while on Archipelago. It increases your odds greatly... although you will probably still 1 continent somewhere & LOTS of ocean.