Minecraft won't load a world when presets for a superflat world is set to ocean

Ok, on Minecraft Java Editon, snap 18w08b, (and snap 18w10a) Minecraft won't create a world for some reason. I have waited like 5 minutes and it still won't load. I cant even close it because it is taking so long. Keep in mind that I'm not using the default launcher, I am using a launcher called TLauncher. Thanks!

• Kye