Hi
Good eye! And nice work so far. This was a club favorite when I started and still one of the better trainers around.
When I built mine the club guys had me leave in the knock outs for the windows in and fill in the front windshield with 1/4" balsa. Cut monokote the same shape as the windows black or silver works. Iron the windows on after the color scheme you use is on. This makes for a much more robust wing mount area also better water (and oil) tightness around the windows. We did a bit of float flying in that club.

I have printed hundreds of BLUE LINE prints and what you are experiencing aside from the weather related factors is "BLUE LINE CREAP". The paper actually slips a bit as it goes through the rollers during exposure to intense light.
The original plan is ink on mylar and it is laid over BLUE LINE paper then the pair is run through a light and roller system. The Ink shades the print paper and that remains, all the clear areas burn off. The paper has to slip a bit in the best case scenario.