I found a hole in the world border that lets me go through.

First I teleported to 2,999,999 ; 60 ; 60. Then I walked through the 3,000,000 and beyond. It started getting laggy and extremely glitchy. Eventually I decided to teleport away to 2,899,999 ; 60 ; 60. However, the lagging and glitchiness remained. I assumed the border of the world is at 3,000,000 however I was able to pass through this barrier.