Most quilting patterns are written with a ¼" seam allowance. Even with a ¼" guide presser foot, each machine is set just a bit differently. For most patterns it is critical that the seams are sewn at the correct measurement.
To test the accuracy of your seam allowance.
If the machine needle is not movable you will need to create an accurate seam guide on the bed of the machine. Place a clear ruler under the presser foot and gently lower the needle until it rests on the marking ¼" from the edge of the ruler. Lower the presser foot to hold the ruler in place. Keeping the ruler perpendicular to the machine bed, carefully align a piece of painters’ tape or Glo Tape along the edge of the ruler and place it on the machine bed. Raise the needle and lift the presser foot to remove the ruler. Test the seam allowance again and reposition the tape as necessary to create and accurate ¼" guide.
Placing more pieces of painter’s tape on top of the first will create a guide the fabric can run along.