Seamless half drop patter

Hi there,

I have a question about half drop seamless pattern. 

1) The pattern I want to make represents 3 swimmers. I set up my first canvas 100x100cm to draw them with vectors. 

2) The second new document I created to turn these swimmer into pattern is 2000x1000pixels. 

 3) I copied and pasted each swimmer into the canvas I created for half drop pattern. Then, all my artwork strokes got thicker and inaccurate, as you can see in the screenshot. 

So I guess I cannot directly copy and paste the element vector based into the canvas pixels based? 

Do I have to rasterise the swimmer first and then copy/paste into the canvas for pattern?

Many thanks again 🙂 

Delphine