I have booked an abortion, what if i get there and change my mind!?

Hi people i made a hasty decision when i went to the doctors the other day out of pure stunned-ness, I feel like i would make the biggest decision of my life and the worst one if i went through with an abortion, anyway i have been booked into an nhs clinic and im worried i will get there and say i can't go through with it, and that people will be rude to me i have two daughters already a four and five year old i know shocking, but i have had two hurrendous pregnancy's ive had hypremissis and last time i was in hospital six months i had a terrible midwife, i just dont know whats going on!