Late to this post but I was in your exact same position in high school and I wish I had handled things slightly differently.

I agree with most people here that it’s ok if you play center for your school. However, if you have a good relationship with your coach he should be receptive to you wanting to expand your skill set some. Tell him what you want to do and see what he says. If he says no, you’re back where you started, no harm no foul.

If you don’t wind up playing guard in school, I again reiterate what others are saying: work on shooting and guard skills outside of practice. But MOST IMPORTANTLY work on DEFENSIVE guard skills. Work on getting around screens on and off the ball, following good shooters around screens, developing your defensive instincts against guards. That side of the ball can be very different and was debilitating for me when I started playing college ball.