I suspect you've changed the "Radius" unit from a DPI-independent setting like "millimeters" or "map units" to "pixels". The sizes look good on a low-resolution screen, but are too small in a high-resolution layout export.
It looks like the scale is set to a high value that makes the view to look smaller. You need to adjust the scale to a smaller value to zoom in to the desired location. Also, you can fix the scale in order to fix the view of the layout to prevent it from being changed.
To do that:
Go to the scale in the layout
Click on Data defined override button