I have a Cross Country Race coming up, and it's about a month away. My Question is when should I start training for this and how should I train? Keep in mind i just came out of a cast.

You should be training NOW. Find a big enough riding area and ride at a consistent pace without any breaks. I’m talking hours. I’m talking till you have to turn on reserve fuel. Consistency is the key. Not getting tired too early. I love running 4 & 5-hour enduros. A lot of guys ride faster but I usually outlast them and place ok. Third in senior class at the Leadbelt Enduro. Ride, ride, ride and then ride.
It's not as much fun if your fighting the bike from being tired. So set your suspension.
HAVE FUN...