I killed a bird accidently with my bb gun how can i live with myself?

I was in my backyard with my bb gun and there was a bunch of little sparrows in a tree and for fun i tried to aim at one not expecting to hit it but i did and it fell to the ground, i ran over there and he was flapping his wing all crazy on the ground and i picked him up and his blood dripped on my hand, there wasnt much blood but it was coming from the back of lower head area and i set him on a cinder block to take a better look and he kept putting his head down and when touched him he jerked his head up like a reaction then after a little put his head back down i was with my friend and we say a little thing of blood on the front and i was confused and my friend says that it went right through his head, then i lost all hope of him living, my mom called my and said to come in for dinner and i am a and couldnt bring myself to putting him out of his misersy so i put on up on this little portable plastic shed so coyotes wouldnt eat him but i have a feeling he will die up there or flutter his wings and fall off then get eaten, i cant even live with myself and i feel so horrible, i am very sensitive guy( 15 by the way) and i feel bad killing bugs even, and now this is too much and i feel ashamed to tell my parents i did this so i didnt tell them, what can i do to make this right because i feel so horrible i cant even explain