China Great Wall is only 3400 miles from east to west

The wall zig zag and climbs up and down with the terrain

It goes in all kinds of directions and ways that it can be longer. If it went straight around, then it wouldn't be as long.

It was intended to protect the "China" of each different era or dynasty from the enemies of that time. Thus the wall sometimes duplicates, sometimes expands, and sometimes abandons regions depending in part on the location of the enemies. So it is really many walls that were constructed over thousands of years going back to the 5th century BC to the time of the Warring States.