Wanna bet?
Draw half along the 45 degree angle. Draw a line from one corner to anther to know where you are flipping along. Draw and remove line. Copy paste half of it into a new paint file, flip horizontally, flip vertically, copy paste into original. Mirrored across the 45 degree angle.
This person knows everything there is to know about paint. She wrote a tutorial on how to do gradients. Could have touched up in photoshop to anti alias, but this lady does the best ms paint work you’ll ever see.
edit
Black and white version.