Don't think that's how it works. Medicine in a lot of cases probably isn't the right course for people.
However, if communication skills is one thing you're concerned about and the only factor affecting your choice to pursue medicine, then I wouldn't be too concerned.
One way which naturally improves communication skills which helped me a whole lot before applying for is volunteering. Even though I am a social person, I had issues when facing new environments which may be unfamiliar eg a hospice or a hospital. After doing volunteering for a few months, I already saw that I am much more comfortable communicating in new situations without much worries about what it's like.
If you're considering applying for medicine, I have no doubt you already have done/planned some volunteering placements. If so, how are they going for you? I'd really recommend doing some volunteering in the summer holidays if you have the time.
Also another thing to note is that you'll have a chance to hone communication skills at university itself as it's an integral part of being a doctor. You'll find that after you ease yourself into medical school, you may find a lot of your worries about shyness may go away as you complete hospital placements and work with peers.
It is natural to feel stressed and timid when entering new circumstances. But it's an extremely rewarding experience. This is especially the case in medicine as once you overcome those fears because you've overcome a small barrier to a thoroughly enjoyable profession. If you believe you enjoy the other aspects of the course, I would advise you to not let that be an obstacle to applying because being successful in medicine involves showing an active interest in the subject as awhole. It is very holistic.
Good luck with your applications, have a good think about your choices and I hope you still continue to go for it!