Side Scrolling help

Hello, I am currently working on a little game and have come across a problem which has held me up for a while now, My game is a side scrolling game, I have a 4800px wide background image. I have tried changing my coding so that the backgound moves and the character stays in the same place which worked quite well except then that kind of broke her jump. I also followed a few bits of coding I have found online but I didn't understand it enough to fix the positioning of the character and keep the UI in place. I am also looking to make the character stop when she hits the edge of the background so you do not just see white. any help appreciated. Here is my current coding:

stop();   //initial lives   var lives:int=3;   //initial score   var score:int=0;   //gravity 'weight'   var gravity:Number = 10;   //jump 'power'   var jumpPower:Number =30;   //is the player already jumpting?   var isJumping:Boolean = false;   //placement of the ground   var ground:Number = 536 - thief_mc.height;     //is player walking?   var isWalking:Boolean = false;   //direction   var direction:Number = 1;   //background scrolling speed   var xScrollSpeed:int = 1;   //sky scrolling speed   var xFarscroll:int = 2;   //tree scrolling speed   var xTreescroll:int = 5;   // listen for key press   stage.addEventListener(KeyboardEvent.KEY_DOWN, onKeyPress);   // listen for key release   stage.addEventListener(KeyboardEvent.KEY_UP, onKeyRelease);   // update stage   stage.addEventListener(Event.ENTER_FRAME, update);   // show score in score box   score_txt.text=String(score);   // show lives in life box   lives_txt.text=String(lives);   //on key press   function onKeyPress(evt:KeyboardEvent):void {   //if you press left, the character walks left   if(evt.keyCode==Keyboard.LEFT){   thief_mc.gotoAndStop("walkleft");   direction = -1;   isWalking = true;   bg_mc.x += xScrollSpeed;   trees_mc.x += xFarscroll;   grass_mc.x += xTreescroll; }   //if you press right, the character walks right   else if(evt.keyCode==Keyboard.RIGHT) {   thief_mc.gotoAndStop("walkright");   direction = 1;   isWalking = true;   bg_mc.x -= xScrollSpeed;   trees_mc.x -= xFarscroll;   grass_mc.x -= xTreescroll;   }     //press spacebar to jump   if(evt.keyCode==Keyboard.SPACE){   if(!isJumping){   jumpPower = 30;   isJumping = true;   } } }   //on key release   function onKeyRelease(evt:KeyboardEvent):void{   //if left arrow released face forward   if(evt.keyCode==Keyboard.LEFT){   thief_mc.gotoAndPlay("idle");   isWalking = false;   }   //if releasing right face forward   else if(evt.keyCode==Keyboard.RIGHT){   thief_mc.gotoAndPlay("idle");   isWalking = false;   } }   //calculation on how high thief_mc jumps as well as where it jumps too.   function update(evt:Event):void {   if(isWalking){   thief_mc.x += direction*10; }   if(isJumping){   thief_mc.y -= jumpPower;   jumpPower -= 2; }   if(thief_mc.y + gravity < ground)   thief_mc.y += gravity;   else{   thief_mc.y = ground;   isJumping = false; }   }