Stress and anxiety are understandable. You legitimately don't know what's going to happen, it could be awesome or it could suck, you've got a lot invested in it, and it will affect your life and the lives of those around you. Paradoxically, I've found that acknowledging and accepting these things tends to decrease my level of stress and anxiety.

Also, commit to doing your best (sounds like you have no problems there), and then you can just remind yourself: "My best will be good enough." You may or may not succeed, but if you remember that you did your honest (and self-examined) best, then you will always be able to be comfortable with yourself.

And finally, a motto: "Clarify by action."