How to join the dots and reduce the dot size in scatter plot using Easychart?
Part of what you're asking for (= "How will I reduce the size of the dots"), is a typical example of how it is like to use a UI (= Easychart), and find out that you need some special option/facility of the Highcharts library, but which you cannot enter via the Easychart UI.

Here are some hints/directions to try to resolve that part of your question anyhow:


As you must have noticed using the Easychart UI, there is nothing (out-of-the-box) that you can use to reduce that size of those dots.
So head over to the Highcharts options reference which outlines the chart configuration options, and the methods and properties of Highcharts objects. Attention: don't get overwhelmed, there are a zillion of options ... in this case, your question boils down to plotOptions.scatter.marker.radius, which is the "radius of the point marker" (don't ask me how I know, I just do ...). It turns out that its defaults is "4". So with that your question becomes like this: How do I overwrite that default value of plotOptions.scatter.marker.radius with (eg) "1"?
To understand where we're going, first have a look at the Feature request Other chart types. It's a request about "Is it possible to use more chart types like Donut, 3d Pie, or any available HighCharts examples". So that is actually way more then just adapting the default value of "radius of the point marker". Nevertheless, comment nr 3 in that feature request contains the actual answer. The crucial part of that comment is that it contains "an example of an interface with more options than those provided by our default set". It takes some effort to digest it (what it is about), but the most important part of that sample is at the end of it, and which looks like so:


{
  "panelTitle": "Advanced Chart options",
  "pane": [
    {
      "title":"Pie/Donut",
      "options": ["plotOptions.pie.innerSize","plotOptions.pie.allowPointSelect","plotOptions.pie.depth","plotOptions.pie.cursor"]
    },
    {
      "title":"3D",
      "options": ["chart.options3d.enabled","chart.options3d.alpha","chart.options3d.beta"]
    }
  ]
}


To understand what this sample is about, have a look at the image in the next comment (nr 4), which looks like so:



As shown in the above image, by adding (near the end) those specifications about "Advanced Chart options", it is perfectly possible to add that panel with title "Advanced Chart options", and with the 2 panes titled "Pie/Donut" and "3D" (each with their related "options" also).