ChartJS - Line Chart - Y axis scale problem ?

Line Chart - Y axis scale problem ?

HTML

<script src="http://www.chartjs.org/assets/Chart.js"></script>
<body>
  <canvas id="chart"></canvas>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.5.0/Chart.min.js"
        integrity="sha256-GcknncGKzlKm69d+sp+k3A2NyQE+jnu43aBl6rrDN2I=" crossorigin="anonymous"></script>

</body>

JavaScript

// Chart
var ctx = document.getElementById("chart");



var options = {
    type: 'line',
    data: {
        labels: [1, 2, 4, 6,7, 10] ,
        datasets: [
            {
                backgroundColor: "rgba(151,187,205,0.2)",
                borderColor: "rgba(151,187,205,1)",
                data: [80, 80, 80, 80, 80, 80]
            },
            {
                backgroundColor: "rgba(220,220,220,0.2)",
                borderColor: "rgba(220,220,220,1)",
                data: [8.84, 17.68, 35.36, 53.04, 70.72, 88.4]
            }
        ]
    },
    options: {
        tooltips: {
            enabled: false
        },
        legend: {
            position: 'top'
        }
    }
};
Chart.plugins.register({
    afterInit: function(chart) {
    var intersect = getIntersection();
    console.log(intersect)
     var datasets = chart.data.datasets;
     var labels = chart.data.labels;
     labels.push(intersect.x)
		labels.sort(function(a,b){return a - b});
    y = labels.indexOf(intersect.x);
    chart.data.datasets.forEach(function(ds,i){ds.data.splice(y, 0, intersect.y)});
   
   }
})
function getIntersection(){
      var y2=17.68, y1=8.84,x2=2,x1=1,x3 = x1, x4 = x2,
          y4=80,y3=80;
      var x=((x1*y2-y1*x2)*(x3-x4)-(x1-x2)*(x3*y4-y3*x4))/((x1-x2)*(y3-y4)-(y1-y2)*(x3-x4));
    var y=((x1*y2-y1*x2)*(y3-y4)-(y1-y2)*(x3*y4-y3*x4))/((x1-x2)*(y3-y4)-(y1-y2)*(x3-x4));
		x = Math.round(x*100)/100;
    y = Math.round(y*100)/100;
    return {x:x,y:y}  ;
    
      /*
       (y-y1)/(x-x1) = y2-y1/x2-x1
       (y - y1)(x2-x1) = (y2 - y1)(x-x1)
       x2y - x2y1 - x1y + x1y1 = xy2 -xy1 - x1y2 + x1y1
       y(x2-x1) - x(y1-y2) = x2y1 - x1y2
       y = (x2y1 - x1y2) +x(y1-y2) /(x2-x1);
       similarly 
        y = (x2y3 - x1y4) +x(y3-y4) /(x2-x1);
        so 
       (x2y3 - x1y4 +x(y3-y4) = (x2y1 - x1y2) +x(y1-y2);
       x(y3-y4-y1+y2) = ((x2y1) - (x1y2)+ (x1y4)-(x2y3))
       var x= ((x2*y1) - (x1*y2)+ (x1*y4)-(x2*y3))/(y3-y4-y1+y2);
       
       
     ...