If you have access to Adobe Illustrator, check out the below on using its repeat feature to make a seamless repeat that will work once uploaded:
Creating a seamless repeat can be tricky if you're just getting started. If you have access to Photoshop, you can do this quite easily using the offset feature.
- Start by setting up your canvas. Be sure to write down the measurements for the center point of your design as you'll need to use it later. For this example, we'll use a 4" square canvas at 150dpi. Begin by creating a design element in the center of your canvas in Photoshop.
- After you've done this, choose Filter > Other > Offset from the main menu.
- In the offset menu, you'll need to enter your center point for the design in either the Horizontal or Vertical box. For this example, enter 2" in the horizontal box within the offset window then click "OK".
- You should now see that your design begins on the left edge of your canvas and is divided in the center with the other half along the right edge of the canvas. You can use the offset option again and enter the measurement into the "Vertical" box to have your design divided into 4 quadrants and placed in the corners of your canvas. After you've done this, simply fill the center of your canvas with the remaining design elements!