Leah,
Of course, it is your baby and YOUR body. How do you feel about the birth? Are you scared that the baby is too big for you? Did you ever question your ability to give birth before that hospital admission?

You have to do what is right for you and your baby. Don't let the doctors dictate to you what will or won't happen.Their advice is important to HELP you make choices.

I won't give you my opinion, but I will tell you a story... I was working in the birthing suite a couple of years ago and a tiny lady came in. She was TINY. Maybe a size 6 and short too. It was her first baby and she didn't look overly large. She was admitted with a history much like yours, niggles and tightenings, low 'period' like pain, radiating into her legs. She was in early active labour when she arrived and laboured throughout the day.
She gave birth to a ten pound baby girl, with no tears! She was amazing! No one knew that her daughter would be so large so no one questioned her ability to birth her baby vaginally. She went into the labour with the expectation that she could/would birth vaginally and she did. Women are AMAZING!

Anyway, hun. I would do some reading and thinking before you make any decisions.