I'm not sure what exactly is going on here but I simply cannot make a map bigger than 8k. I've uninstalled all java versions. Made sure I downloaded the x64 version and installed it. Used the batch file to increase my heap size to 12GB using -Xmx12G. But every time I go to make the map it gets to the 2nd exporting point after having generated the world, gets to about 3.9GB (4.1GB if using the .exe version) and then hits a memory exception.
Pictures here: https://imgur.com/a/nwIHjjq
[EDIT]
NEVERMIND! FIXED IT!!! God damn it took me long enough. Turns out it was the "Picked up _Java_Options: Xmx4G" that was ♥♥♥♥ing with it. Turns out there was for some reason this was added to the System Variables which was overiding any and all increases to RAM that I gave java. If anyone else is noticing they have this too, this link will help fix it:
[/EDIT]