Brilliant job! This was a great work! Sort of slow at first, in terms of pacing (not tempo), but it quickly got quite interesting around the first tempo change to 42 bpm (my favorite tempo...because it's 42 . Overall great treatment of the subject, lots of variety and different stops used to create an eerie and discomforting environment. While overall the writing for organ was great, I felt you could have used more extremes, low ranges and high ranges, pedal notes, as well as just more or volume in places (meaning more or fewer notes, being an organ. The swell pedal could have also been used...period). There was some of that towards the end, and I thought it was really effective. I would've liked to see more of it throughout the piece.
The organ is the king of instruments, but here it's treated more like the prince.
Amazing job overall, though, I really hope you did well in the competition!