preview now shows up in top left of it's box, needs to be centred

assignments/a2/src/main/java/Sidepane.java

@@ -108,6 +108,7 @@ class previewPanel extends JPanel
         }
       });
     this.preview = new previewLine(m);
+    this.setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
     this.add(preview);
     this.add(slider);
   }