Can I use this program to make it so only specific biomes spawn in the world?

I am attempting to make a modpack in which I make the entire world an ocean for me and my friends. I have been painstakingly trying to figure out how to make an ocean only world for 3 days and I have gotten no where. I tried making a custom dimension which worked but the structures I wanted did not spawn. (ie. Monument, ocean ruins etc) so does anyone know how I can figure this out?