Madigan, glad that you are going for the natural option. Even if you only labour for a little while it is much better for you and the baby than an elective section.
Just to reiterate what everyone else has said, I recovered from my birth far quicker than my friends did, they had all had C-sections for one reason or another.
I'm quite petite and I managed fine. I just went in without a doubt that I could do it, after all the human race wouldn't be here if most of us weren't capable of giving birth, so try not to worry too much. And one of my mates, who is quite small too, gave birth to a 9lb 9oz baby the other week in the birth pool at the local hospital and she didn't even need stitches or pain killers!
If I was you I would read as much as you can yourself and don't rely too heavily on the advice from your consultant or mw. The more informed you are the more confident you should feel.
And don't forget what everyone else has said about the scans being wrong, saw my MW today and she said its not uncommon for them to be 2lbs out, so that would mean you could be having a 7lb baby!
Also, I've heard too that bigger babies are easier to push out but don't know why.
Do everything you can to make yourself feel more relaxed, I've been doing pregnancy yoga for the last few weeks and this has given me lots of confidence. They teach you breathing and positions that really help with pushing those babies out.
Two things you haven't mentioned, and you don't have to answer of course, is there a reason that you are under a consultant and are you going on any ante-natal courses?
Oh, and one last thing, I'm due in August too, have you have a look in the Ante-natal Clubs at the due in August thread, they are a really nice bunch.
Good luck and I've got every faith that you can do it!