I know that you might be dreading tellings your parents, but in the long run its for the best because they will find out sooner or later, and they will still love you!
Maybe you should sit down with your mum first, im sure she'll understand. Theres no easy way to say it, but once its out in the open the hardest bit is done! They might initially be mad, but they'll forgive you!
Just tell them, everything will work itself out so dont spend more time worrying about it!