Please don't worry! If you have a bit of luck and the baby is in the right position, and you can just let your body go with the flow, it needn't be that bad, honestly.
I read up a lot on the primitive brain and childbirth, read Yehudi Gordon's book (good for early baby info too), and recommend Nicole Croft's book on childbirth (she was my ante-natal yoga instructor and fab she was too).
I listened to a hypnobirthing track a few times. It sounded a bit bonkers to me but funnily enough I used a lot of the breathing and visualisation techniques during my labour - it really helped. I also did yoga and Pilates to 40 weeks so was strong and fit - good as I stayed on hands and knees for the whole labour!
My labour was only 8 hours from first contraction to birth, and that was slowed considerably by an unexpected health issue with me. No drugs, just TENS, back massage, and hands and knees position. I honestly wouldn't say it was 'painful' but the contractions took over my whole body and mind - it was completely absorbing.
Your hormones and endorphins are designed to build gradually to give your body chance to cope. Go with the flow, use gravity to help, and get into whatever position that works for you (ideally not on your back with knees up as the coccyx then narrows the birth canal). With a bit of luck you might find it's not nearly as bad as you fear.
My best tip is hope for the best, plan for the worst (figure out what you will do if advised that intervention could be necessary), and coach your birth partner to be your advocate to speak for you while you're busy doing your thing.
Good luck 