First time doing cross country and I have some questions?

I am doing my first cross country show on the 10th July. I have been riding for 8 years and do 3- 3 6 jumpers/equitation. Thought it would be good for both my horse and me to get out there just once and try something new. If I jump 3 6 at home would it be ok to do beginner novice?(2-2 7) Do you have any advice? I have never ridden cross country before and don't know what it's like. Is it any different from hunter/jumper? How was your first time doing cross country? My mare has never refused a fence with me so should be worried like going through water? Should I canter the whole thing or trot hills some jumps?