I know how you feel - I was exactly the same when I was your age. I had no particular interests (academically speaking) at school, so when it came to applying to Uni, I felt that I had to lie about my "passion" for a subject that I really wasn't interested in. That's exactly what I ended up doing. I chose to study what I was good at (which happened to be Maths & Physics) and spent four years doing a degree that I didn't enjoy. Do I regret it? No. University was the best time of my life. I had great fun, made some awesome lifelong friends who I shared some incredible experiences with, and I ended up getting a qualification that helped me land a job with a starting salary of £35k.
Let me quickly address a couple of misconceptions for you:
1.) University is not all about studying a subject you're passionate about. It's about a million things more than that. It's about being independent and having loads of great experiences, it's about learning about life and maturing, it's about making friends and forging networks. My degree was only 5% of what I got out of Uni, and I'm glad it was that way.
2.) You don't have to be passionate about your subject and do it as a pastime activity to achieve good results. I'm probably a good example of this actually... I didn't like Maths or Physics, but I graduated with a 1st class honours degree. I'm not particularly clever either - you just need to do the right amount of work at the right time (i.e. cram in the third term each year before exams) and you can spend the rest of your time having fun.
3.) Your subject is not necessarily going to define your career. Most graduates end up in jobs that bear little relevance to their degree. The biggest graduate employers are those offering training contracts and they usually employ graduates of any discipline. Many of your peers will end up as accountants, bankers, management consultants, retail managers etc having done nothing relevant to those careers at Uni. The important thing is to make the most of your time at Uni, have fun, and get a good degree. You can worry about work later.
To finish, I thought I'd tell you the rest of my story. I have now, finally, found a real genuine passion. Having never even considered it at school, I have now returned to University and am studying Medicine as a second degree, which I absolutely love. I feel like it's my true calling and I couldn't be happier to be at Medical School. It's not uncommon for people to find their true passion later on in life, so if you haven't discovered it by age 18, don't worry. Just take things as they come, be flexible, work hard, have fun, and make the most of the opportunities that present themselves. If you want to go to Uni to study a subject you don't enjoy, go for it, maybe it'll take you somewhere you never expected