Not suggesting you do this entire thing (especially not in a school) but it might be worth seeing if the magnets override the error in the short term
This comes from: Upgrade to pro, cost, slot mod
You see where the top magnet is on this image? With your doors closed, try placing a magnet there (on both the left and right sides) - it may fool the machine into fixing itself. If it’s truly a cable issue then it won’t (shouldn’t?) work because it’s the signal that it’s closed that’s not making it - but if it does work that may provide support with additional info
Good luck