help with biome generation pls

Hi, I'm trying to create a biome for my mod, I want it to be fairly flat and take up a large area. I've been experimenting with the continentalness, weirdness and erosion values for a few days now and I think I've got the values right, but my biome is generating underground under the minecraft:plains biome. I understand that minecraft:plains is replacing my biome and this happens absolutely all the time. Is there a way to solve this?