If you're feeling nervous, it's okay to talk to your trainer about it. Take a step back, do some pole work up and down the hill, and jump smaller fences. Work on your position, your distances, and build up your confidence. But in the end, the only way to get over your jumping anxiety is to overcome your fears. At some point, you've just got to do it. In the meantime, work on the basics. Sometimes I learn more from jumping cavalettis and crossrails than a 3 foot fence. It's about the overall journey, and it's okay if you're having a few hiccups along the way as long as you don't give up!