I was in exactly the same boat as you 2 years ago when DS1 was born.
As soon as i did the pregnancy test and got the BFP I though 'This baby will have to come out in 9 months'.
DH and I were both 8lb something at birth and I was terrified of how big our baby would be.
Scans told me DS would be around 8lb so I thought fine, only 1lb over the average.
I did lots of reading so I knew what to expect once labour begand and made sure I understood how contractions worked etc (though I find it all very facinating, others may find it boring!) I always had my nose in a book.
I made a birth plan, made sure DH knew what I wanted and DS1 was bron in water in the hospital. During the birth I felt very confident. You must keep your mind positive and confident and be confident that your body can do it even when your brain is saying run to the hills, woman, get out of here!!
DS1 was 9lb9.5 born.
As he was my first, the way it went and his weight seemed normal to me. To me he was tiny, but to everyone else there, he was huge.
When I fell pregnant with DS2, I did not get an overwhelming panic or anything and did not worry about giving birth.
I had scans that said they thought he would be 11lb+, then I got a bit worried as they said if they thought he exceeded 11 by 40 weeks they would arrange a section for me which I really did not want.
In the end I went for days over and gave birth within 24 hours of having a sweep after being told I had 48 hours, then if no baby, they would induce me via a drip, then possibly CS if no luck.
As with DS1, DS2 was born in the same pool at the hosp. only 14m later and it all went well.
During transistion though, I began to let the pain get the better of me and said I couldn't do it and was going to die but the MW who I really liked and was there for DS1s birth also, told me firmly but politely to pull myself together as I was not helping myself or the baby getting hysterical and that everything would be okay.
It was okay and DS2 was 10lb12.5 without a scratch to my dainty bits.
In conclusion, both times were fine and I actually enjoyed giving birth. It is so exciting!
The way they spook you with 'OMG your baby is going to be HUGE!' especially to first timers is terrible I think. I don't think they should really say anything as usually they are wrong and unless the baby really is HUGE, there is seldom any reason birth should be a prob.
Try not to get worked up about it. What I kept in my mind was that as DS1 was my first I didn't know any better, so hey ho!
You will be fine.