Having taught a class for my guild several times on piecing 4" Mariner's Compass blocks for name tags, I can make some suggestions. First, carefully press each seam as you go--finger pressing leads to distortion later. When pressing, I don't use steam--also can lead to distortion. To get a nice sharp edge, use a small brush to put a bit of starch or sizing (spray some into the plastic cap of the can of starch) right along that seam. When ready to sew the wedges of the compass together, use Sharon Schamber's method to use Elmer's Washable School Glue, heat-set, to hold the wedges together perfectly when you sew--using pins can lead to distortion. Pop the glue loose and carefully press the seam of the two wedges open to reduce bulk. I wish I'd known about the glue before teaching those classes, would have dropped the frustration level enormously for my friends.
Pat in Rockport, TX