It happens because bubbles require some space to represent itself and axisX actually starts from the value of first dataPoint and ends at value of last dataPoint. If you don’t want to clip the bubbles, you can change minimum and maximum values of axisX. This new changed value depends upon the size of first and last bubble size.
var min = chart.axisX.get("minimum");
var max = chart.axisX.get("maximum");
chart.axisX.set("minimum", min - 1);
chart.axisX.set("maximum", max + 1);
You can check with subtracting and adding different values instead of 1 to meet your requirement.