New End Gateways not created when dragon is killed

I killed the dragon and no gateway appeared so I reset the end, killed the dragon and had a gateway appear. The gateway took me to a small island with no buildings or other features so I created the crystals to respawn the dragon. When I killed it this time, no new end gateway appeared and I go to the same island. I've tried getting to another island by crouching and building a bridge using blocks but I get to the edge of the world force field or whatever and can't go anywhere else. Do I have to reset the end again or what should I try? I'd like to go visit some of the other areas in the end, if possible. Thanks.