Unless your doctor has told you not to exercise, you should be getting regular exercise.
If you are physically active your heart will grow stronger and will not beat as fast.
It is especially important at your age when your body is developing.
There are always ways to exercise although our society makes it harder all the time. Nobody walks anywhere anymore. If you are able to walk to school, do it. Don't get a ride. Walk with some friends. Even if it is 2 miles, that's only about 40 minutes.
Join a school sport, anything that gets you moving and your heart beating.
It'll eat into your gaming time, but at your age you'll start seeing the muscles growing and becoming more defined quickly.
I have always been into long distance running and as a result I have a very low heart rate. I was recently in a first aid course and the other people in my group were shocked at my heart rate. If I hadn't been so active throughout my life it wouldn't be that way.
Good luck. You can do it.