For access to the attic, my house had a 22" square drywall board.
I managed to break it in half over the weekend. Is there anything
in the fire codes (I live in Maryland) that limits what they can
be made of?

The reason I ask is because I had a spare sheet of plywood in
my garage. I've trimmed it to the correct size, put joint compound
on it to get the texture to match the ceiling's, and primed and
painted it. The paint is drying right now.

However, it occured to me that using a wooden board may violate
some kind of fire code. Is there anything wrong with what I've
done?