I had the same problem with my Mossberg 835, only mine was shooting even higher.I bought some TruGlo Magnum Gobble Dot Pro-Series sights and fixed the problem. They cost around $40-$45. Lucky for me a local sporting goods store had them 1/2 off when I went to buy them.

As others have said, don`t aim for the head, aim at the middle of the neck. Now, having said that, you still want the best part ofyour guns pattern to be centered where you aim. I would try the TruGlos or put a low power scope or a Red Dotscope on it.