To go or not to go

I`m in a dilemma. I`ve been asked by a friend several weeks ago, to go to an event with her on Friday evening, its about 20 miles from where I live, and I`ve said yes, because I want to go to it with her. But I still haven`t managed to pluck up the courage to tell my parent that I`m going. There`s nothing wrong with the event, and nothing wrong with the friend, but I know my parent will object because of me driving on my own late at night because she`ll worry herself sick about it. It`s beginning to play my nerves up and make me feel unwell. Or, am I feeling a bit like this because in the back of my mind her worry about my driving late at the weekend is also a worry to me? Do I tell my friend I can`t go and make excuses, although she`s probably got the tickets now? Do I go and worry my parent for the evening? I`m torn between the two.