[Mjaw]

I need to close this up as the light fixture that I will be using has a small base that nearly covers the box.

I tried hot mud and paper tape but it sagged and I just took it down as I wasn't confident that it would hold up. View attachment 42073

Fill with some hot mud , mix it stiff/pretty dry , pack it lwt it harden then shave it flat then tape

 

[Mjaw]

Tape it, give it 2 coats, stretch each coat a little further