I clicked the button to activate "in-room descriptions" and entered my in-room description for my object, but it is just listed as a normal object, not given the description. How do I fix this? Thank you.

The description is not necessarily part of the object, just something that is part of the room description. If it does not show up as part of the room description, try including it in the 'look at' description, the actual room description, or as part of a non-default prefix and suffix for the object. It might also be possible that it didn't save before you played the game, or some other issue like that.
I hope this helps!

For some reason, in-room descriptions don't work in rooms whose description is a script. Could this be the problem?

If so, add the line:

msg (GetRoomDescription())

to the room's description script, where you want the in-room descriptions to appear.

mrangel solved the problem! Thank you!