I was a shy person. You would never know it now, but once upon a time, I was horribly shy. I just had to make up my mind that it was silly to be shy. What is the worst that can happen? You do something stupid and they LAUGH at you? OH NO!!! HORRORS!!! Not the dreaded LAUGH!! Anything but that!! Now have a good laugh. Go ahead laugh at your self. You can't live your life being worried what everyone else thinks about you, even a cute boy that you like.
The point is, what do YOU think about YOU? Make a list of your good qualities and concentrate on the good things about yourself to help you gain self confidence. Now, practice NOT being shy. Yeah, practice. Look in the mirror and have a conversation with the boy that you like. Tell "him" that you like him. Then say all the terrible, embarrassing things that you imagine he might say. Take another long look in the mirror to see if you are still alive and ok. Yep! being embarrassed, even by an imaginary boy did not kill you. You can even laugh about it. Then practice again. Practice talking to this boy until you feel comfortable with it.
We all fear rejection. Being rejected is not the end of the world. It is just the end of that moment and there are many, many more moments to come in life. This is just one moment. One great moment does not mean that all the rest of your life will be equally great, like wise one bad moment does not mean that the rest of your life will be bad. You never know, this boy might be shy too and does not know what to say to you. You might start off by telling him that you like him a little more than just being friends. He will respond that he either likes you a lot or that he just wants to stay friends. Either way, you will know. The main thing is to keep the friendship and tell him so. Go practice in the mirror. It really helps get over being shy.
If you want to be a good ball player, you must practice. if you want to play in the band, you have to practice. If you want to not be shy anymore, you have to practice. There is no magic fairy that will zap you with a magic wand to make your shyness go away. Do you have a friend that is shy too? Maybe you two could practice on each other. You can get over being shy, but you will have to work at it and not let it ruin your day if things aren't perfect. Wish you the best.