Should I go to England?

I recently decided I should go to England to visit a friend for three weeks. I am 24 years old, live in the USA and have never left the country before. I will be traveling alone. I'm suddenly really really nervous and am having doubts about the trip. I am scheduled to leave this Monday!! I thought it would be good for me but now I am realizing I might be making a mistake. Any insight or opinions will really help me. I need to decide by this Saturday morning in order to get a credit on the airfare. Thanks :)