The tighter-spaced dots at the beginning of each line are the mirrors starting to accelerate. Plus, maybe some ringing and burn-in at the end of the lines when the mirrors come to an abrupt stop.
The left side of the edge appears to show white dots, which indicates a too long “Laser Off TC”.
Can you run these two files, please?
This will show the different timings. (They have bi-directional disabled, so that each line interval starts on the left and ends on the right side.)
laser ON TC calibration-negative.lbrn2 (66.4 KB)
laser Off TC calibration-Aa.lbrn2 (65.4 KB)
Oh, and: Increasing the “Polygon TC” (Time spent in the corners) should make the edges pointier.
More background info in this thread.
For a complete calibration of the Timing settings, I recommend this video from MakrTheory