cluelessgoon, same story here; I knew about 'cross in my teens, but I'm in my mid-30s and only first racing it now.
There's been a lot of good feedback here as far as training, so here's what I'll add:
- Get out of the gym and be solely on the bike. Make sure you can ride hard for a 40-minute period. Also, condition yourself by riding to the point where your heart is racing, legs are burning, and breathing is maxxed, then let off the effort for a little bit, try to gain control of your breathing and heartrate as quickly as possible, then up the effort again to the max-out point before dropping off and regaining control again. This, basically, is 'cross racing, for 40 minutes.
Otherwise, it sounds like you're doing a good job of getting yourself prepared. In addition to the ride training, you'll also need to get yourself prepped for race day, including showing up two hours before your race and riding the course as much as possible to know what's out there and how to handle it. Ride the course at a slow warmup pace and at race pace. Riding through a section and racing through it are two different things, so get to know and master the course before you race it.
Get a good warmup and get to the start line ten minutes before the race starts. This way, your body is ready to go, and you know what lays ahead for the next forty minute of hell...I mean...er...fun!
Seriously, good luck and we all look forward to reading a race report.