Scan both sides of your layout and save them to your computer.

Open both sides in the software program.

Go to Image>Resize and resize each half of the image. Set the Height to 700 pixels, and make sure that Resize type is set to Smart Size from the drop down menu. Set the resolution to 72 dpi.

Open a new image - Select File>New from the menu, using 1000x1000 pixels. This will give you a large area to work on.

Choose one half of your layout, then Edit> Copy. Click on your new image, then choose Edit, Paste As New Layer. Do the same with the second half. You now should have your two halves in the new image area.

Move the halves around, lining them up on top of each other until they match. You can zoom in if you need to.

Crop around the edges and save your new image as .jpg.

Resize image with the dimensions being no larger than 500x500. After resizing, check the file size, it should be 100 kb or less. If not, resize dimensions again.