Just a simple error.
I found no reason to treat the chart as Transverse Mercator. The limiting longitudes are parallel, indicating a Mercator Chart. Changing the header to PR=MERCATOR, sorted the chart out.
Alternatively, if you insist that this is a T Merc chart, the PP value is wrong. You have it based on the latitude, which is OK for Mercator Charts
. For Transverse Mercator charts
you have to use the average longitude of the eastern and western edge.
I have not tested this approach. The end result is likely to be close, as well but probably not as good as just changing the header, described above.