Juguemos tiro al blanco!

¡Hola!, les comparto el código del tiro al blanco que realicé, para realizarlo estuve leyendo un poco sobre setInterval aqui: https://developer.mozilla.org/en-US/docs/Web/API/setInterval

No logré superar el nivel 3 y el puntaje de 1100, ¡a ver si alguien puede superarlo!. El código:

<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">

<canvas width="800" height="600"></canvas>

<script>
    var canvas1 = document.querySelector("canvas");
    var paint_brush = canvas1.getContext("2d");
    var area_x = 0, area_y = 100;
    var area_width = canvas1.width - area_x;
    var area_height = canvas1.height - area_y;
    var targetRadius = 30;
    var score = 0;
    var level = 1;
    var speed = 2000;
    var clicks = 0;
    var targetX = randomInt(30,770);
    var targetY = randomInt(130,570);
    var ID;

    function createTargetArea(){
        paint_brush.fillStyle = "black";
        paint_brush.fillRect(area_x,area_y,area_width,area_height);
    }

    function createMarkArea(){
        paint_brush.fillStyle = "darkgrey";
        paint_brush.fillRect(0,0,canvas1.width,canvas1.height-area_height);
        paint_brush.fillStyle = "black";
        paint_brush.font = "50px verdana";
        paint_brush.fillText("|Nivel:"+level+" |Puntaje:"+score,10,70);

    }

    function drawCircle(x,y,radius,color){

        paint_brush.fillStyle = color;
        paint_brush.beginPath();
        paint_brush.arc(x,y,radius,0,Math.PI*2);
        paint_brush.fill();
    }

    function drawTarget(x,y){
        drawCircle(x,y,30,"red");
        drawCircle(x,y,20,"white");
        drawCircle(x,y,10,"red");
    }

    function randomInt(lowerLimit,upperLimit){
        let result;
        while(true){
            result = Math.round(Math.random()*(10**(((upperLimit).toString().length))));
            if (result >= lowerLimit & result <= upperLimit) {
                return result;
                break;
            }
        }
    }    

    function targetHit(event){
        console.log(event);
        let click_x = event.x - canvas1.offsetLeft;
        let click_y = event.y - canvas1.offsetTop;
        if((click_x >= targetX-10 & click_x <= targetX+10)&
            (click_y >= targetY-10 & click_y <= targetY+10)){

            clicks ++;
            if(clicks >= 3){
                level++;
                clicks = 0;
                clearInterval(iD);
                iD = setSpeed();
            }
            score += 100*level;
            speed = speed / level;
        }
    }

    function starGame(){
        targetX = randomInt(30,770);
        targetY = randomInt(130,570);
        createMarkArea();
        createTargetArea();
        drawTarget(targetX,targetY);
    }
    function setSpeed(){
        return setInterval(starGame,speed);
    }
    createMarkArea();
    createTargetArea();
    iD = setSpeed();
    canvas1.onclick = targetHit;
</script>

Quedo atento a comentarios para mejorarlo y seguir aprendiendo.