Pattern Making

I'm currently working on a pattern within an artboard that I will make a repeating grid pattern. I'm having lots of trouble making it seamless. I'm a beginner in both Illustrator and pattern making. I've looked up videos on how to make my pattern seamless and figured the best way was to put objects on the border of my artboard and copy them to the exact location on both the sides and the top and bottom of the artboard. The issue is, in all the examples I've found using this method, the pattern sample on their artboard isn't symettrical like mine so they can easily adjust the material inside their artboard to fit the objects on the borders. My pattern can't be adjusted within the artboard as its symettrical and will look off if I adjust material to fit the objects on the border. Does anyone know how I can solve this issue? Also the artboard for my pattern is a rectangle not a square if thats at all significant.