Fix the background being too small during export when zoomed out

macrovision.js

@@ -663,7 +663,7 @@ function drawScales(ifDirty = false) {
     ctx.scale(deviceScale, deviceScale);
 
     ctx.beginPath();
-    ctx.rect(0, 0, canvas.width, canvas.height);
+    ctx.rect(0, 0, ctx.canvas.width / deviceScale, ctx.canvas.height / deviceScale);
     ctx.fillStyle = "#333";
     ctx.fill();