It is entirely understandable if you may experience anxiety or flat-out fear over labour and the birthing process. We believe you can overcome this fear. Look at the following and see if anything might help you a bit on your way.
Is it possible for you to trace your fear? Knowing what is keeping you from relaxing might help you. You might also look up vaginismus to see if this holds some of your issues. It is possible to come to terms with fear issues like people with phobias do. You might need to talk it through with a therapist. It is wiser dealing with the problem in the beginning than at the end of pregnancy.
See if you can find an experienced midwife who you trust to have in reserve +to support you.