Describe the Bug

I was changing from my survival game to create a new creative world. In doing so I accidently pressed the preview world and then immediately canceled and after tried to load the world as a super flat which took forever to load so I exited the program after about 10 minutes at 99%. After I closed Minecraft I relaunched It and to find my survival world replaced with a creative world.

Reproduction Steps

1. Exit from a preexisting world
2. In the Single player menu click create new world
3. Open the Preview menu then immediately click cancel
4. Set the world to super flat (I wanted a superflat world so it may work with others)
5. Create the new world
6. Exit the program at 99% and reload Minecraft
7. Worlds may be swap with the creative one

Expected Result

I expected to have a second world that being a creative world

Screenshots and Videos

No response

Crash Report or Log

No response

Operating System

Windows 11

Mod Version

0.3.2g

Minecraft Version

1.16.5

Forge Version

36.2.20

Other Mods

I was using the Create a beyond modpack from CurseForge

Additional Context

No response