It's so normal to worry about it... but helps if you consciously tell yourself to calm down, you've done it before, and close your eyes and visualise a positive birth, a relatively easy birth, a good outcome.

Breathe... breathe in and count to four while inhaling, then while exhaling try a longer count, like to 6 or 8 or even 10... this exercise slows your heart rate a little and invokes calm. I do this in labour too. Very helpful. Once you practice and get used to it, you can use this to calm yourself down very quickly.

For what it's worth I'm currently feeling lots of tightenings too, I've had my show, am feeling it's all going to happen soon, even though I'm only just 37 weeks. I have had a 9lb5oz baby too, but my 2nd birthing experience was much easier, smaller baby and quick labour, so I try to visualise that and not dwell on the tougher labouring experience!

trust your body's ability and try to relax in everything you do. You can always yell for an epi if and when you need it.

Good luck, hope it all goes smashingly well!