I would do three things, and then I could pretty much promise you won't miss again.

1) Stay cool under pressure. Try not to get nervous to he point where your shakin' like a whore in church. Position yourself so you can use your knees or something as a gun rest (this is the hardest of the three)

2) Pattern your gun to make sure your hitting where you suppose to at 15 yards.

3) Change your sites. Put a fixed power scope on your gun. I have a gun set up strickly for turkey hunting, look into it.