it isn't unheard of, why put yourself through something for the next three years if you don't want to do it? It doesn't matter that you've had a gap year already, you should be where you want to be at the end of things. Personally I think it would be a lot more sensible if you took another gap year and reapplied to a course you really want to do. But make sure whatever you reapply to IS what you want to do, so you don't have to go through all this again! And you should be able to get a loan and things, I know plenty of people who have dropped out of courses at about Christmas time because it wasn't for them, and they are much happier for it and all the money stuff got sorted out.
Your parents might misunderstand, but just explain to them. In the end, it's YOUR life and it's YOU who isn't happy. It's not like you're saying you don't want to do anything at all, I don't see why they shouldn't be happy with your choice. I hope it all works out. : )