The only advice I might give here is your interval and DPI are not in sync. If the interval is to small you can end up with overlapping pixels in the software rendition of the scan so you can end up with a heavier line.
Of course could be something completely different.
Try this as a start point : DPI / 25.4 = X then X / 3 = interval (DPI = Dots per INCH)
150dpi = 0.17 interval
200 = 0.13
250 = 0.1
There is not much point having an image over 250/300 dpi max as your laser dot cannot go small enough to generate a burnt image with that many dots that are not overlapping.
hope that helps.