As much as it might seem unrelated, maybe look into having a birth attendant (sometimes called a doula) or doing some birth education classes other than the hospital ones (Calmbirthing is great for alleviating any doubts about your birthing abilities). The reason I suggest it is that your body and mind can sometimes interfere with each other and never is this more true than in labour! Your body knows what it needs to do and it'll do it as long as your mind doesn't stop it with anxiety, fear, worry etc. A birth attendant is great for re-focusing you if things get a little hectic or not-exactly-according-to-plan. She'll be calm, experienced and able to help you through any anxieties you might be having.

PS: congrats on your pg!