Creating a tileable mesh I'm trying to model a simple curtain, which will need to be tiled horizontally. How can I make sure it looks well when tiled?

Here's a video about the problem:

https://youtu.be/51uqrzNm0Q8
Been trying this on and off for some time. For this particular mesh, if the shape is that simple, you can just copy the mesh, and flip it the other way, whichever axis it goes across, scale it to -1