fix canvas height

 let app = getApp();
 const windowWidth = app.globalData.systemInfo.windowWidth;
 const windowHeight = app.globalData.systemInfo.windowHeight;
-const screenHeight = app.globalData.systemInfo.screenHeight;
+let screenHeight = app.globalData.systemInfo.screenHeight;
 
-const scale = windowWidth / 375;
+const canvasWidth = 375;
+const canvasHeight = 667;
+
+const scale = windowWidth / canvasWidth;
+
+screenHeight = windowWidth / (canvasWidth / canvasHeight);
 
 var Point = function(x, y) {
   return {