How do I damage Polaroid i-type film?

I am doing an odd thing with Polaroid i-type film, but that's what I need it for.

In brief, I try to expose it outside of the camera, then insert into "Polaroid Now" in order to develop.

The question: what causes the large spoiled spot in the corner (see the attachment)?

The procedure:

- pull a sheet from cartridge

- expose in DIY enlarger while the picture area being squeezed between two plates (glass and plastic); the "pod" and the "trap" not touched

- insert the sheet into an empty cartridge

- insert the cartridge into "Polaroid Now" camera

- "take" a picture without flash and with lens being obstructed

- let the photo develop face-down on a table

Thank you in advance,

Oleg.

The spot is where developing chemicals didn't reach.

The two smaller spots look like dirt on the rollers, which might also be related to above.