It's not how you fold it, it's how you place it on the die. Take a piece of masking tape and tape it over the last 1/4" or so of the blades. Make sure that it is exactly 90 degrees to the blades. Fold a piece of newspaper and place the fold exactly against the tape. Cut. Check the paper. Keep readjusting the tape until the paper comes out perfectly straight. Now take a sharpie marker (use silver for black foam) and mark the edge of the tape & remove it. Now you have a guide so you can place the fold of your fabric exactly perpendicular to the blades and will get straight cuts.