I did this - In my first year I chose horrid subjects (maths, further maths, chemistry, physics, critical thinking) which didn't suit me at all. Ended up with a D in Maths A level, a C in chemistry, didn't take the exam in physics, and managed to scrape a B in critical thinking.
I was soooooooo close to giving up on college all together, but decided to go back, with a totally new attitude and completely different subjects. Now, I've just left college with A* Politics, A* Psychology, A* English Language and B in Philosophy, and I'm going on to study Politics and Philosophy at Exeter.
Starting again was definately worth it for me =]