I wanted to be a dancer or a photographer.
With age comes wisdom.
You shouldn't be worrying about that now. Especially the UKCAT score on your personal statement. God, I didn't even know about the admissions tests til last summer.
Also, doctors and vets are completely different, when you're older you'll need to decide which you want to do most. You have to care about the things you're going to help, rather than just think it looks fun, because it's not fun, it's fulfilling. It's also generally not exciting, it's nothing like Casualty or ER or the animal hospital programmes on the TV. Usually people are either "people" people, or "animal" people so be careful not to get those confused.
You need to think more about the present rather than 4 years time, though.