If you aren't feeling comfortable, there is usually a very good reason. In your case, it seems as though you are not comfortable at high speeds yet. No matter how much you do not fear heights, this is only a small part of successfully completing jumps. My suggestion to you would be, stay out of the park for a little and get really comfortable at high speeds. Without that comfort, there is no way that you are ever going to be comfortable on jumps because clearing jumps requires speed. Don't rush into anything. The key to park riding is having good fundamentals.