How do I get out of it?

In Minecraft Pixelmon I went through an ultra gate and can't get out like that?

All you have to do is jump into the void and you will be teleported back to the normal world. Alternatively, these portals that you used to get there will also spawn from time to time, they will then lead you back again. But the easiest way, as I said, is to just jump into the void.