They have a witness service here in scotland which i was a volunteer for a short while, hopefully english courts have them also, they will alay your fears when you come to court, but i suggest that you get in contact with them before you come to court they are fantastic in making sure your appearance in court is as smooth and painless experience!
Dont worry, hun, you won't be asked what you "think" if you're there to give evidence- the court will only be interested in what you "know" for certain x