Are you using a checkering tool, or a carving tool? A key when checkering is to make multiple passes, and don't try to do your run all at once. It's almost like sketching with a pencil pushing the tool back and forth as you run your line. But it has to be a saw type checkering tool. File type only work by pushing. Until you train your hand, you can use a good straight edge and an exacto blade make your initial line, then run your checkering tool in the groove.
