Congratulations. I also recently did my first mtb race. It was at a ski resort and had some hard climbs but it was lots of fun. I missed the beginner class start so I had to race in the Intermediate class. Everyone was super nice and I didn't finish last which was my goal. I spend more time on my road bike than my mountain bike so it was an adjustment for me.
It was 18 miles and I finished in 2:08. A lot of people were walking up the 4 mile climb up the side of the mountain but I stayed on my bike for the most part. The downhill was a blast...it was hard to see in the shade of the trees. I just looked for the dust from the guy in front of me.
Lots of fun but I'm not sure if I'll do it again.