var chart = new Chart(ctx, {
   type: 'line',
   data: {
      labels: ['Jan', 'Feb', 'Mar'],
      datasets: [{
         label: 'LINE',
         data: [3, 2, 4],
         backgroundColor: 'rgba(0, 119, 290, 0.2)',
         borderColor: 'rgba(0, 119, 290, 0.6)'
      }]
   },
   options: {
      responsive: false,
      scales: {
         yAxes: [{
            afterFit: function(scale) {
               scale.width = 20  //<-- set value as you wish 
            },
            scaleLabel: {
               display: true,
               labelString: 'y-axis label',
            }
         }]
      }
   }
});